[Tutor] Occurrence of number 2 in a range from 1 to 100
Hi, How can we write a logic for detecting the number 2 in range from 1 to 100 Regards, Reuben ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Alternatives to append() for growing a list
On Sun, Dec 1, 2013 at 5:04 PM, Steven D'Aprano st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 02:32:38PM +1000, Amit Saha wrote: Hello, I was told by someone (as a comment) that a code snippet such as this would make Pythonistas talk my ear off about how evil the append() function is: There is absolutely nothing wrong with append. Either you have misunderstood, or the person who told you this was smoking crack. heh, no I literally quote the person above, so I think I understood him alright. mylist = [] mylist.append(1) # a number of times over However, growing a list one item at a time using append like this is too much hard work. Some better solutions: # You have an existing list, and want to append a bunch of things to it mylist.extend([x, y+1, z*2]) # You want a list consisting of the same objects repeated many times mylist = [0, 1, 2]*100 # like [0, 1, 2, 0, 1, 2, 0, 1, 2, ...] # You want to create a list containing known objects mylist = [1, 2, 4, 8, 16, 32, 64] # Like above, but using a list comprehension mylist = [2**n for n in range(7)] # You don't know how many things you want to add. mylist = [] x = 1 while x 100: mylist.append(x) x = 3*x-1 and so on. As you can see, append has its job to do. The last case is the closest to the context in which I used the above code construct. I have some ideas that on an append() the list's internal size increases (doubled?) since CPython over-allocates memory, and such. Not just on append. Any operation that adds or deletes items from a list might trigger a re-size. If the list needs to increase, it will double in size up to some maximum, then it will grow by a smaller amount. The purpose of this is that *on average* appending to the list will take a fixed amount of time. So, the question is: what is the alternative to growing a list when I have no idea what items or how many may be there? Don't worry about growing the list. That's all handled for you as part of the list interface. The whole point of using Python is to not have to worry about internal details like that. Right, that's what I thought. Good that I checked here, now I can write a nice reply to the comment :-) Thanks Steven and Dave. Best, Amit. -- http://echorand.me ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
Hello, On Sun, Dec 1, 2013 at 3:50 PM, Reuben reuben.dl...@gmail.com wrote: Hi, How can we write a logic for detecting the number 2 in range from 1 to 100 You question is unclear. Could you please give more details ? Best, Amit. -- http://echorand.me ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Loop over floating point values
Hello, Much to my disbelief, I realized I hadn't written a program in Python as far as I can recall which required me to do something like this, in psuedocode: x = 0.1 for i = 0 to x step 0.01 # do something with i end i Simply stated, I want to start from say a value, 0 and go upto 0.1 in increments of 0.01. I don't want to create a list with the values hard-coded and then iterate over it, and hence I would use a while loop instead: x = 0.1 while i x: # do something with i i += 0.01 I think this is one case, where you definitely cannot do this with a for loop assuming the following restrictions: - Do not create a list of the floating point values as i=[0.01, 0.02, 0.03..] - either like that or by using a suitable mathematical formula combined with a list comprehension - Use numpy's linspace() to create the list for you Thoughts? Thanks, Amit. -- http://echorand.me ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On Sun, Dec 01, 2013 at 11:20:02AM +0530, Reuben wrote: Hi, How can we write a logic for detecting the number 2 in range from 1 to 100 2 in range(1, 101) -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Loop over floating point values
Hi, - Do not create a list of the floating point values as i=[0.01, 0.02, 0.03..] - either like that or by using a suitable mathematical formula combined with a list comprehension You could simply write your own version of xrange that does it, as a generator: def xrange_f(start, stop, step): x = start while x stop: yield x x += step Then, in your code, you can do: for f in xrange_f(0, 10, 0.01): pass -nik -- * concerning Mozilla code leaking assertion failures to tty without D-BUS * mirabilos That means, D-BUS is a tool that makes software look better than it actually is. PGP-Fingerprint: 3C9D 54A4 7575 C026 FB17 FD26 B79A 3C16 A0C4 F296 signature.asc Description: Digital signature ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Loop over floating point values
On Sun, Dec 01, 2013 at 07:03:15PM +1000, Amit Saha wrote: Hello, Much to my disbelief, I realized I hadn't written a program in Python as far as I can recall which required me to do something like this, in psuedocode: x = 0.1 for i = 0 to x step 0.01 # do something with i end i Such floating point loops are tricky to get right, thanks to rounding of floats. Observe: py x = 0.0 py while x 1.0: ... x += 0.1 ... py x == 1.0 False py x 1.0999 We expect that after the loop is done, x should equal 1, but it doesn't. That means that it actually loops one time too many. One way to fix this is to iterate over integers, and then divide just before doing the work: for x in range(0, 10): print x/10.0 Another way is to use the recipes I have here: http://code.activestate.com/recipes/577878-generate-equally-spaced-floats/ http://code.activestate.com/recipes/577881-equally-spaced-floats-part-2/ http://code.activestate.com/recipes/577068-floating-point-range/ I encourage you to read all three. If you have any questions, please feel free to ask. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On Sun, Dec 01, 2013 at 02:57:33PM +0530, Reuben wrote: I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit The most efficient way is to use a bit of reasoning: 2, 12, 20 through 29, then 32, 42, 52 etc. But if you have to do it computationally: for i in range(1, 101): print 2 in str(i) -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Loop over floating point values
On 01/12/2013 09:14, Dominik George wrote: Hi, - Do not create a list of the floating point values as i=[0.01, 0.02, 0.03..] - either like that or by using a suitable mathematical formula combined with a list comprehension You could simply write your own version of xrange that does it, as a generator: def xrange_f(start, stop, step): x = start while x stop: yield x x += step Then, in your code, you can do: for f in xrange_f(0, 10, 0.01): pass -nik To encourage Python 3 take up this should be range rather than xrange :) -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On 01/12/2013 05:50, Reuben wrote: Hi, How can we write a logic for detecting the number 2 in range from 1 to 100 Regards, Reuben Paper and pen or pencil should be perfectly adequate for this task. Alternatively, open an editor, type some code, run it, if you have problems ask another question here, preferably one that makes sense :) Unless of course your question above is to be taken literally, in which case Mr. K'Aprano has already answered. -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On Sun, Dec 01, 2013 at 08:43:46AM -0500, bruce wrote:
hmm...
two questions. (new to cmdline py)
tried typing in what was typed in above in the python shell:
for i in range(1, 101):
print 2 in str(i)
this did nothing..
Curious. Which Python shell did you use?
I would expect that you get a prompt (without the quotes). I've
changed the prompt in my Python to py, but by default you should have
. Then, when you hit return at the end of the first line, you
should get the second level prompt, You'll need to add at least
one space, or tab, to indent the second line. Then when you hit enter
again you'll get a ... prompt, Enter one last time and the code will
run. Here's what I get (changing 101 to a smaller number for brevity:
py for i in range(1, 11):
... 2 in str(i)
...
False
True
False
False
False
False
False
False
False
False
However, I may have inadvertently been misleading. Outside of the
interactive shell, even though that code will run, it won't display any
output. Only in the interactive shell does that print True and False as
above.
Outside of the interactive shell, you need to use the print statement or
function to see the output, otherwise Python calculates the answer and
then doesn't do anything with it. So it may be better to write this as:
for i in range(1, 101):
print (2 in str(i))
which will work anywhere.
def aa():
for i in range(1, 101):
print 2 in str(i)
aa()
error::
aa()
Traceback (most recent call last):
File stdin, line 1, in module
NameError: name 'aa' is not defined
That is remarkable. I cannot explain this error. Are you using IDLE or
some other shell?
the other question, what does the in function within py do?? I've
used str.find() to look if a substring is present, but didn't know a
in even exists..!
The in operator tests whether one object includes another object. For
example, with strings it tests substrings:
hat in what
= returns True
hat in h-a-t
= returns False
With lists and tuples, it tests to see if an item is the given value:
23 in [1, 5, 23, 99]
= returns True
dog in [cat, dog, mouse]
= returns True
dog in [cats, dogs, mice]
= return False
But it only looks one level deep!
23 in [1, 2, 3, [22, 23, 24], 5, 6]
= returns False
With dictionaries, it checks to see if the given object is a key:
5 in {2: two, 5: five, 7: seven} # {key: value}
= returns True
but not a value:
five in {2: two, 5: five, 7: seven}
= returns False
--
Steven
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Re: [Tutor] Alternatives to append() for growing a list
On Sun, Dec 1, 2013 at 2:04 AM, Steven D'Aprano st...@pearwood.info wrote: might trigger a re-size. If the list needs to increase, it will double in size up to some maximum, then it will grow by a smaller amount. The purpose of this is that *on average* appending to the list will take a fixed amount of time. Here's the over-allocation rule: if newsize 0: const = 3 if newsize 9 else 6 newsize += newsize // 8 + const Starting from empty and appending: 0, 4, 8, 16, 25, 35, 46, 58, 72, 88 CPython's list uses realloc, which tries to resize without copying. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On Sun, Dec 1, 2013 at 6:14 AM, Steven D'Aprano st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 02:57:33PM +0530, Reuben wrote: I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit The most efficient way is to use a bit of reasoning: 2, 12, 20 through 29, then 32, 42, 52 etc. [n for n in range(100) if n % 10 == 2 or n // 10 == 2] [2, 12, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 32, 42, 52, 62, 72, 82, 92] Floor division (//) and modulo (%) are explained here: http://docs.python.org/2/reference/expressions.html#binary-arithmetic-operations ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On 01/12/2013 17:40, eryksun wrote: On Sun, Dec 1, 2013 at 6:14 AM, Steven D'Aprano st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 02:57:33PM +0530, Reuben wrote: I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit The most efficient way is to use a bit of reasoning: 2, 12, 20 through 29, then 32, 42, 52 etc. [n for n in range(100) if n % 10 == 2 or n // 10 == 2] [2, 12, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 32, 42, 52, 62, 72, 82, 92] Floor division (//) and modulo (%) are explained here: http://docs.python.org/2/reference/expressions.html#binary-arithmetic-operations I wish people would use Python 3 references. I believe it would lead to a greater take up of, IMHO, a superior product than Python 2. -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On Sun, Dec 1, 2013 at 12:53 PM, Mark Lawrence breamore...@yahoo.co.ukwrote: On 01/12/2013 17:40, eryksun wrote: On Sun, Dec 1, 2013 at 6:14 AM, Steven D'Aprano st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 02:57:33PM +0530, Reuben wrote: I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit This way may not be faster, but it may be simpler to understand: for n in range(100): ... if '2' in str(n): ... print n ... ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor -- Joel Goldstick http://joelgoldstick.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On 01/12/2013 17:59, Joel Goldstick wrote: On Sun, Dec 1, 2013 at 12:53 PM, Mark Lawrence breamore...@yahoo.co.uk mailto:breamore...@yahoo.co.uk wrote: On 01/12/2013 17:40, eryksun wrote: On Sun, Dec 1, 2013 at 6:14 AM, Steven D'Aprano st...@pearwood.info mailto:st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 02:57:33PM +0530, Reuben wrote: I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit This way may not be faster, but it may be simpler to understand: for n in range(100): ... if '2' in str(n): ... print n ... Why do you appear to be replying to me but haven't quoted anything that I've said? It's also difficult to see who said what above as the normal attribution marker levels are missing. Time to boot google products into touch? As for code speed who cares? Good programmers jump that fence when they have to, not because they can. -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] truncated dictionary return
I have a script that reads sensor values gathered by an Arduino board from
serial as a dictionary, said values to later be used in the AI for Nav
Control. Here's the script:
#!/usr/bin/python
def sensorRead():
import serial
from time import sleep
sensors = {}
sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
Temperature Humidity Light'.split())
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
d = {}
for item in line.split(','):
item = item.strip()
key, value = item.split(':')
key = key.strip()
value = value.strip()
d[key]=int(value)
return d
I hope that comes through okay, I copied it from the text file so
indentation and such should be fine, if not let me know.
The script works great with one exception. I understand the problem, I'm
just not sure how to address it. The problem is:
The Arduino runs on a constant loop, it reads each sensor, sends the key
and the value to the serial bus in format for python to read it as a
dictionary, lather, rinse, repeat.
Python querries the bus when told. Usually the python script gets the full
dictionary (all 8 values with keys, brackets etc) but sometimes it doesn't.
Sometimes it only gets the last few values, sometimes it gets nothing or
misses a bracket and throws an error. This makes sense. They are not in
sync.
What I need to figure out how to do is have the python script wait until
the next round of values as signified by the opening bracket { or check
that it has all 8 values and if not retry or something.
Would this be an if/else? try? exception?
I've not yet delved into any of these in my quest to learn python except
if/else and that doesn't feel right for this, so I'm at a loss as to how to
proceed.
regards, Richard
--
*Mater tua criceta fuit, et pater tuo redoluit bacarum sambucus*
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Re: [Tutor] truncated dictionary return
richard kappler richkappler at gmail.com writes:
I have a script that reads sensor values gathered by an Arduino board from
serial as a dictionary, said values to later be used in the AI for Nav
Control. Here's the script:
#!/usr/bin/python
def sensorRead():
import serial
from time import sleep
sensors = {}
sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
Temperature Humidity Light'.split())
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
d = {}
for item in line.split(','):
item = item.strip()
key, value = item.split(':')
key = key.strip()
value = value.strip()
d[key]=int(value)
return d
The script works great with one exception. I understand the problem, I'm
just not sure how to address it. The problem is:
The Arduino runs on a constant loop, it reads each sensor, sends the key
and the value to the serial bus in format for python to read it as a
dictionary, lather, rinse, repeat.
Python querries the bus when told. Usually the python script gets the full
dictionary (all 8 values with keys, brackets etc) but sometimes it doesn't.
Sometimes it only gets the last few values, sometimes it gets nothing or
misses a bracket and throws an error. This makes sense. They are not in sync.
What I need to figure out how to do is have the python script wait until
the next round of values as signified by the opening bracket { or check
that it has all 8 values and if not retry or something.
There should be no sync issue here. The readline method should read from the
serial port until it reaches an EOL character, then return the whole line
(i.e., your sleep(1) should be removed since readline() already waits for
input).
From what you're describing, the real issue seems to be on the side of the
sender. Are you sure, it terminates each line with \n as it should? Where is
that code coming from?
Best,
Wolfgang
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Re: [Tutor] truncated dictionary return
Hi again,
think I spotted the problem now:
you’re setting up your connection everytime you enter the function (with the
serial.Serial call), but I guess you’re calling that function repeatedly to
retrieve lines. That’s wrong and means you could loose data that was sent
while you weren’t listening.
You’ll have to open the connection once outside the sensorRead() function,
then pass it the arduino object like this:
def sensorRead (arduino):
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
# rest of your code
# your main program:
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
while True:
reads = sensorRead(arduino)
# do something with the data
Hope that helps,
Wolfgang
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Re: [Tutor] truncated dictionary return
Wolfgang Maier wolfgang.ma...@biologie.uni-freiburg.de wrote in message
news:loom.20131201t230651-...@post.gmane.org...
richard kappler richkappler at gmail.com writes:
I have a script that reads sensor values gathered by an Arduino board
from
serial as a dictionary, said values to later be used in the AI for Nav
Control. Here's the script:
#!/usr/bin/python
def sensorRead():
import serial
from time import sleep
sensors = {}
sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
Temperature Humidity Light'.split())
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
d = {}
for item in line.split(','):
item = item.strip()
key, value = item.split(':')
key = key.strip()
value = value.strip()
d[key]=int(value)
return d
The script works great with one exception. I understand the problem, I'm
just not sure how to address it. The problem is:
The Arduino runs on a constant loop, it reads each sensor, sends the key
and the value to the serial bus in format for python to read it as a
dictionary, lather, rinse, repeat.
Python querries the bus when told. Usually the python script gets the
full
dictionary (all 8 values with keys, brackets etc) but sometimes it
doesn't.
Sometimes it only gets the last few values, sometimes it gets nothing or
misses a bracket and throws an error. This makes sense. They are not in
sync.
What I need to figure out how to do is have the python script wait until
the next round of values as signified by the opening bracket { or check
that it has all 8 values and if not retry or something.
There should be no sync issue here. The readline method should read from
the
serial port until it reaches an EOL character, then return the whole line
(i.e., your sleep(1) should be removed since readline() already waits for
input).
From what you're describing, the real issue seems to be on the side of the
sender. Are you sure, it terminates each line with \n as it should? Where
is
that code coming from?
Best,
Wolfgang
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I also suspect sleep doesn't work. Two better options would be:
1. read/loop until line terminator,
2. Use serial signals, i.e., RTS/DTS if possible.
Paul Simon
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Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On 12/01/2013 06:50 AM, Reuben wrote: Hi, How can we write a logic for detecting the number 2 in range from 1 to 100 Do you mean: if 2 in numbers: ? Also for a more general solution, think at the very nice function any(bools), in combination with a generator comprehension: numbers = [2,3,4,5,6,8] if any((n%2 == 1) for n in numbers): print(some is odd) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Alternatives to append() for growing a list
On 12/01/2013 05:32 AM, Amit Saha wrote: Hello, I was told by someone (as a comment) that a code snippet such as this would make Pythonistas talk my ear off about how evil the append() function is: mylist = [] mylist.append(1) # a number of times over I have some ideas that on an append() the list's internal size increases (doubled?) since CPython over-allocates memory, and such. So, the question is: what is the alternative to growing a list when I have no idea what items or how many may be there? Maybe you are confusing with catenating _strings_, rather than lists. Python's concat is problematic because it is a binary operation. So, catenating n bits makes n-1 operations, each with intermediate results, of growing sizes, all thrown away except for the last one, the actual result. If all of the bitN are strings: bit1 + bit2 + bit3 + bit4 + bit5 actually constructs: bit1+bit2 bit1+bit2+bit3 bit1+bit2+bit3+bit4 bit1+bit2+bit3+bit4+bit5 A number of unneeded string object, and a very big useless memory weight. Example Python code showing good/bad usage below (advanced pythonistas, please correct if needed, I don't know the latest nice Python idioms): # === case of a series of explicite text sections # don't do this: text = intro = intro... text += intro body = body... text+= '\n' + body concl = concl... text += '\n' + concl print(text) ; print() # also do not do: text = intro + '\n' + body + '\n' + concl print(text) ; print() # do that...: intro = intro... body = body... concl = concl... text = '\n'.join([intro, body, concl]) # but creates a list print(text) ; print() # ...or that: text = %s\n%s\n%s % (intro, body, concl) # no such list print(text) ; print() # === case of a list of sections of arbitrary size # (simulation code for demo) def make_section (n): return %s\n % n section_data = [13, 5, 79, 4, 268, 0, 987654321] # don't do this: text = for dat in section_data: section = make_section(dat) text += section print(text) # do that...: sections = [] for dat in section_data: section = make_section(dat) sections.append(section) text = ''.join(sections) print(text) # ... or that: sections = (make_section(dat) for dat in section_data) text = ''.join(sections) print(text) # ... or even that: text = ''.join(make_section(dat) for dat in section_data) # no need for ((...)) print(text) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
I tried it with the python interpreter as mentioned below:
test@test-Inspiron-1564:~/learn$ python
Python 2.7.4 (default, Apr 19 2013, 18:28:01)
[GCC 4.7.3] on linux2
Type help, copyright, credits or license for more information.
On Sun, Dec 1, 2013 at 7:50 PM, Steven D'Aprano st...@pearwood.info wrote:
On Sun, Dec 01, 2013 at 08:43:46AM -0500, bruce wrote:
hmm...
two questions. (new to cmdline py)
tried typing in what was typed in above in the python shell:
for i in range(1, 101):
print 2 in str(i)
this did nothing..
Curious. Which Python shell did you use?
I would expect that you get a prompt (without the quotes). I've
changed the prompt in my Python to py, but by default you should have
. Then, when you hit return at the end of the first line, you
should get the second level prompt, You'll need to add at least
one space, or tab, to indent the second line. Then when you hit enter
again you'll get a ... prompt, Enter one last time and the code will
run. Here's what I get (changing 101 to a smaller number for brevity:
py for i in range(1, 11):
... 2 in str(i)
...
False
True
False
False
False
False
False
False
False
False
However, I may have inadvertently been misleading. Outside of the
interactive shell, even though that code will run, it won't display any
output. Only in the interactive shell does that print True and False as
above.
Outside of the interactive shell, you need to use the print statement or
function to see the output, otherwise Python calculates the answer and
then doesn't do anything with it. So it may be better to write this as:
for i in range(1, 101):
print (2 in str(i))
which will work anywhere.
def aa():
for i in range(1, 101):
print 2 in str(i)
aa()
error::
aa()
Traceback (most recent call last):
File stdin, line 1, in module
NameError: name 'aa' is not defined
That is remarkable. I cannot explain this error. Are you using IDLE or
some other shell?
the other question, what does the in function within py do?? I've
used str.find() to look if a substring is present, but didn't know a
in even exists..!
The in operator tests whether one object includes another object. For
example, with strings it tests substrings:
hat in what
= returns True
hat in h-a-t
= returns False
With lists and tuples, it tests to see if an item is the given value:
23 in [1, 5, 23, 99]
= returns True
dog in [cat, dog, mouse]
= returns True
dog in [cats, dogs, mice]
= return False
But it only looks one level deep!
23 in [1, 2, 3, [22, 23, 24], 5, 6]
= returns False
With dictionaries, it checks to see if the given object is a key:
5 in {2: two, 5: five, 7: seven} # {key: value}
= returns True
but not a value:
five in {2: two, 5: five, 7: seven}
= returns False
--
Steven
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Re: [Tutor] Loop over floating point values
On 12/01/2013 10:03 AM, Amit Saha wrote: Hello, Much to my disbelief, I realized I hadn't written a program in Python as far as I can recall which required me to do something like this, in psuedocode: x = 0.1 for i = 0 to x step 0.01 # do something with i end i Simply stated, I want to start from say a value, 0 and go upto 0.1 in increments of 0.01. I don't want to create a list with the values hard-coded and then iterate over it, and hence I would use a while loop instead: x = 0.1 while i x: # do something with i i += 0.01 I think this is one case, where you definitely cannot do this with a for loop assuming the following restrictions: - Do not create a list of the floating point values as i=[0.01, 0.02, 0.03..] - either like that or by using a suitable mathematical formula combined with a list comprehension - Use numpy's linspace() to create the list for you Thoughts? There is a general solution for this (a typical school problem ;-), maybe the reason why we rarely meet it in practice!). However, watch the issues with binary floats mentionned by Steven. # loop from x0 to x1 with step dx, total n passes x0, x1, dx, n = -0.3, 0.8, 0.2, 6 for i in range(n): x = x0 + dx * i print(x) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Hash map and dictionaries
Hi Question 1: - I would like to know the concept of hash map. Additionally, I got to know that hash maps are equivalent to dictionaries in python. I would like to understand the relationship between dictionaries and hash map better. Question 2: -- It is also said that in a list of may be 10,000 elements(specifically integers), hash maps would be a better option to find the occurrence of repetitive integers How can this be implemented using dictionaries for a list of 10,000 integer elements? Regards, Reuben ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit On 01-Dec-2013 2:45 PM, Steven D'Aprano st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 11:20:02AM +0530, Reuben wrote: Hi, How can we write a logic for detecting the number 2 in range from 1 to 100 2 in range(1, 101) -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
Thanks everyone for all the replies. On Sun, Dec 1, 2013 at 11:29 PM, Joel Goldstick joel.goldst...@gmail.comwrote: On Sun, Dec 1, 2013 at 12:53 PM, Mark Lawrence breamore...@yahoo.co.ukwrote: On 01/12/2013 17:40, eryksun wrote: On Sun, Dec 1, 2013 at 6:14 AM, Steven D'Aprano st...@pearwood.info wrote: On Sun, Dec 01, 2013 at 02:57:33PM +0530, Reuben wrote: I mean occurrence of 2 from numbers 1 to 100. The number could be the first digit or second digit in a two digit number..for e.g. In number 21 it appears as first digit. For number 92 it appears as second digit This way may not be faster, but it may be simpler to understand: for n in range(100): ... if '2' in str(n): ... print n ... ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor -- Joel Goldstick http://joelgoldstick.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Fwd: empty delimiters, and None
The answer is , yes (to both questions)
locale -a does report availability of en_US (and en_US.UTF), C is supported,
but C.UTF-8 does not appear in the list.
I have tried inserting export LANG=en_GB.UTF.8 as a new line 127.
Thanks.
-A
-Original Message-
From: eryksun eryk...@gmail.com
To: uga...@talktalk.net
CC: Tutor@python.org
Sent: Sat, 30 Nov 2013 23:56
Subject: Re: empty delimiters, and None
On Sat, Nov 30, 2013 at 7:04 AM, uga...@talktalk.net wrote:
believe the system locale is set correctly:
Apples-iMac-4:~ apple$ locale
LANG=en_GB.UTF-8
Does `locale -a` report that en_US is available?
127
6) Insert a new line before line 127 with this content:
export LANG=en_US.UTF-8
Did you try en_GB.UTF-8 here?
Lines 123 to 127 of the launcher script read:
# NOTE: Have to add .UTF-8 to the LANG since omitting causes Inkscape
# to crash on startup in locale_from_utf8().
export LANG=`grep \\`echo $LANGSTR\`_\ /usr/share/locale/locale.alias | \
tail -n1 | sed 's/\./ /' | awk '{print $2}'`.UTF-8
echo Setting Language: $LANG 12
The current version uses the value of AppleCollationOrder or
AppleLocale (e.g. defaults read .GlobalPreferences AppleLocale) to
find the locale in the locale.alias file, and defaults to
en_US.UTF-8. I don't know if en_US is always available in OS X,
but surely C.UTF-8 would be. I don't know why it can't modify the
existing LANG to use the UTF-8 codeset. Finally, I can't speak for OS
X, but the glibc locale.alias on Linux is obsolete and doesn't have an
alias for English.
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Re: [Tutor] empty delimiters, and None
Well, yes. I find can indeed use;locale.setlocale(locale.LC_ALL) thanks! In addition to locale.setlocale(locale.LC_ALL, None) I found I can also use; locale.setlocale(locale.LC_ALL, 'en_GB') The question remains, why does; locale.setlocale(locale.LC_ALL, '') fail, especially if it is good practice? -A -Original Message- From: spir denis.s...@gmail.com To: tutor@python.org Sent: Sun, 1 Dec 2013 0:56 Subject: Re: [Tutor] empty delimiters, and None On 11/29/2013 02:19 PM, uga...@talktalk.net wrote: I have also looked at locale.py Line 494 of which is the last line of a def (def function?) I include this below, hopefully this may save you searching for locale.py (Pyhon 2.6) should you need it and wish to answer the above questions, it may help. def setlocale(category, locale=None): Set the locale for the given category. The locale can be a string, a locale tuple (language code, encoding), or None. Locale tuples are converted to strings the locale aliasing engine. Locale strings are passed directly to the C lib. category may be given as one of the LC_* values. if locale and type(locale) is not type(): # convert to string locale = normalize(_build_localename(locale)) return _setlocale(category, locale) As a side-note, in addition to what other have said, the headline of the function def def setlocale(category, locale=None) says that None is the default (standard) value for the parameter 'locale'. This means that, if ever you provide no value for it when calling setlocale, then the value None is used in standard. So, you could as well call it like: locale.setlocale(locale.LC_ALL) # no value at all for param 'locale' instead of you correction locale.setlocale(locale.LC_ALL, None) for the initial version locale.setlocale(locale.LC_ALL, '') This is actually good coding practice (in all language which have default values). Denis ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] truncated dictionary return
On 12/01/2013 08:28 PM, richard kappler wrote:
I have a script that reads sensor values gathered by an Arduino board from
serial as a dictionary, said values to later be used in the AI for Nav
Control. Here's the script:
#!/usr/bin/python
def sensorRead():
import serial
from time import sleep
sensors = {}
sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
Temperature Humidity Light'.split())
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
d = {}
for item in line.split(','):
item = item.strip()
key, value = item.split(':')
key = key.strip()
value = value.strip()
d[key]=int(value)
return d
I hope that comes through okay, I copied it from the text file so
indentation and such should be fine, if not let me know.
The script works great with one exception. I understand the problem, I'm
just not sure how to address it. The problem is:
The Arduino runs on a constant loop, it reads each sensor, sends the key
and the value to the serial bus in format for python to read it as a
dictionary, lather, rinse, repeat.
Python querries the bus when told. Usually the python script gets the full
dictionary (all 8 values with keys, brackets etc) but sometimes it doesn't.
Sometimes it only gets the last few values, sometimes it gets nothing or
misses a bracket and throws an error. This makes sense. They are not in
sync.
What I need to figure out how to do is have the python script wait until
the next round of values as signified by the opening bracket { or check
that it has all 8 values and if not retry or something.
Would this be an if/else? try? exception?
I've not yet delved into any of these in my quest to learn python except
if/else and that doesn't feel right for this, so I'm at a loss as to how to
proceed.
* What is the point of the 'sensors' dict? (also, you don't need to initialise
it as an enmpty dict)
* If you know about regexps or another matching utility, use that to decode the
input line into (key,value) pairs. This is even easier if input has a strict
format. Would tell us?
* About wrong input (incomplete data), avoid try/except, except if ever most
cases are ok (it is very costly in case of exception). Anyway, you need to
decode input, so use that to check for errors/missing stuff.
If you used a matching tool, its absence of result would directly tell about
wrong input (provided your pattern is correct! ;-) As of now, just place checks
in your decoding sequence. Possible checks places, at first sight, marked below:
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
# check line not empty
# (actually big enough for at least {} + one key:val entry)
d = {}
# first get items in separate var and check how many:
for item in line.split(','):
item = item.strip() # not needed, for you strip key/val again
later
# first get tuple from split() and check its size is 2
key, value = item.split(':')
key = key.strip()
value = value.strip()# not needed, for int() itself strips
# maybe one try/except here for checking conversion to int:
# (else, you need to check yourself it is an int numeral)
d[key]=int(value)
Each check failure is a sign of wrong input. What do you need to do, then?
Abandon the whole round?
Denis
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Re: [Tutor] Occurrence of number 2 in a range from 1 to 100
On 01/12/2013 18:02, Reuben wrote: Thanks everyone for all the replies. No problem but please don't top post, it makes following long threads particularly difficult, thanks. -- Python is the second best programming language in the world. But the best has yet to be invented. Christian Tismer Mark Lawrence ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] truncated dictionary return
Now I'm completely lost. While opening the serial port outside the function
sounds like a good idea, I'm thinking that might not work unless I am
mistaken. The sensorRead function once it's called would then basically own
the serial port barring other traffic, yes? That won't work as the same
serial port that receives sensor data from the arduino sends propulsion and
nav signals to the arduino which, along with controlling/reading the
sensors, also controls the motors used for propulsion, hence only opening
the port when the data is called for. The sensorRead function works, heck
it's not even mine, it was written by one of the gurus here in response to
a question I posed months ago (either Alan or Eryksun IIRC) and does
exactly what it's supposed to do, except for the timing bit.
Perhaps I'm looking for a simple solution where none exists but I rather
doubt it. I was thinking something along the lines of (psuedo code here)
check incoming dict for length or number of elements
if 8, keep
else retry
While I appreciate the above comments and any help that is offered, I
neither understand them as presented nor think they will fix the problem
with the limited understanding I do have. Again, it could be my lack of
knowledge is preventing me from seeing the light here, but it feels like
we're reinventing the wheel.
I hope that didn't come across as rude, it truly was not intended to be
such.
regards, Richard
On Sun, Dec 1, 2013 at 3:06 PM, spir denis.s...@gmail.com wrote:
On 12/01/2013 08:28 PM, richard kappler wrote:
I have a script that reads sensor values gathered by an Arduino board from
serial as a dictionary, said values to later be used in the AI for Nav
Control. Here's the script:
#!/usr/bin/python
def sensorRead():
import serial
from time import sleep
sensors = {}
sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
Temperature Humidity Light'.split())
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
d = {}
for item in line.split(','):
item = item.strip()
key, value = item.split(':')
key = key.strip()
value = value.strip()
d[key]=int(value)
return d
I hope that comes through okay, I copied it from the text file so
indentation and such should be fine, if not let me know.
The script works great with one exception. I understand the problem, I'm
just not sure how to address it. The problem is:
The Arduino runs on a constant loop, it reads each sensor, sends the key
and the value to the serial bus in format for python to read it as a
dictionary, lather, rinse, repeat.
Python querries the bus when told. Usually the python script gets the full
dictionary (all 8 values with keys, brackets etc) but sometimes it
doesn't.
Sometimes it only gets the last few values, sometimes it gets nothing or
misses a bracket and throws an error. This makes sense. They are not in
sync.
What I need to figure out how to do is have the python script wait until
the next round of values as signified by the opening bracket { or check
that it has all 8 values and if not retry or something.
Would this be an if/else? try? exception?
I've not yet delved into any of these in my quest to learn python except
if/else and that doesn't feel right for this, so I'm at a loss as to how
to
proceed.
* What is the point of the 'sensors' dict? (also, you don't need to
initialise it as an enmpty dict)
* If you know about regexps or another matching utility, use that to
decode the input line into (key,value) pairs. This is even easier if input
has a strict format. Would tell us?
* About wrong input (incomplete data), avoid try/except, except if ever
most cases are ok (it is very costly in case of exception). Anyway, you
need to decode input, so use that to check for errors/missing stuff.
If you used a matching tool, its absence of result would directly tell
about wrong input (provided your pattern is correct! ;-) As of now, just
place checks in your decoding sequence. Possible checks places, at first
sight, marked below:
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
# check line not empty
# (actually big enough for at least {} + one key:val entry)
d = {}
# first get items in separate var and check how many:
for item in line.split(','):
item = item.strip() # not needed, for you strip key/val
again later
# first get tuple from split() and check its size is 2
key, value = item.split(':')
key = key.strip()
value = value.strip()# not needed, for int() itself strips
# maybe one try/except here for checking conversion to int:
# (else, you need to check yourself it is an int numeral)
d[key]=int(value)
Each check failure is a sign
Re: [Tutor] truncated dictionary return
Would something like
if len(dict) = 8
return d
else
continue
work?
On Sun, Dec 1, 2013 at 8:54 PM, richard kappler richkapp...@gmail.comwrote:
Now I'm completely lost. While opening the serial port outside the
function sounds like a good idea, I'm thinking that might not work unless I
am mistaken. The sensorRead function once it's called would then basically
own the serial port barring other traffic, yes? That won't work as the same
serial port that receives sensor data from the arduino sends propulsion and
nav signals to the arduino which, along with controlling/reading the
sensors, also controls the motors used for propulsion, hence only opening
the port when the data is called for. The sensorRead function works, heck
it's not even mine, it was written by one of the gurus here in response to
a question I posed months ago (either Alan or Eryksun IIRC) and does
exactly what it's supposed to do, except for the timing bit.
Perhaps I'm looking for a simple solution where none exists but I rather
doubt it. I was thinking something along the lines of (psuedo code here)
check incoming dict for length or number of elements
if 8, keep
else retry
While I appreciate the above comments and any help that is offered, I
neither understand them as presented nor think they will fix the problem
with the limited understanding I do have. Again, it could be my lack of
knowledge is preventing me from seeing the light here, but it feels like
we're reinventing the wheel.
I hope that didn't come across as rude, it truly was not intended to be
such.
regards, Richard
On Sun, Dec 1, 2013 at 3:06 PM, spir denis.s...@gmail.com wrote:
On 12/01/2013 08:28 PM, richard kappler wrote:
I have a script that reads sensor values gathered by an Arduino board
from
serial as a dictionary, said values to later be used in the AI for Nav
Control. Here's the script:
#!/usr/bin/python
def sensorRead():
import serial
from time import sleep
sensors = {}
sensors = dict.fromkeys('Sonar1 Sonar2 Sonar3 Sonar4 Dewpoint
Temperature Humidity Light'.split())
arduino = serial.Serial('/dev/ttyACM0', 9600)
sleep(1)
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
d = {}
for item in line.split(','):
item = item.strip()
key, value = item.split(':')
key = key.strip()
value = value.strip()
d[key]=int(value)
return d
I hope that comes through okay, I copied it from the text file so
indentation and such should be fine, if not let me know.
The script works great with one exception. I understand the problem, I'm
just not sure how to address it. The problem is:
The Arduino runs on a constant loop, it reads each sensor, sends the key
and the value to the serial bus in format for python to read it as a
dictionary, lather, rinse, repeat.
Python querries the bus when told. Usually the python script gets the
full
dictionary (all 8 values with keys, brackets etc) but sometimes it
doesn't.
Sometimes it only gets the last few values, sometimes it gets nothing or
misses a bracket and throws an error. This makes sense. They are not in
sync.
What I need to figure out how to do is have the python script wait until
the next round of values as signified by the opening bracket { or check
that it has all 8 values and if not retry or something.
Would this be an if/else? try? exception?
I've not yet delved into any of these in my quest to learn python except
if/else and that doesn't feel right for this, so I'm at a loss as to how
to
proceed.
* What is the point of the 'sensors' dict? (also, you don't need to
initialise it as an enmpty dict)
* If you know about regexps or another matching utility, use that to
decode the input line into (key,value) pairs. This is even easier if input
has a strict format. Would tell us?
* About wrong input (incomplete data), avoid try/except, except if ever
most cases are ok (it is very costly in case of exception). Anyway, you
need to decode input, so use that to check for errors/missing stuff.
If you used a matching tool, its absence of result would directly tell
about wrong input (provided your pattern is correct! ;-) As of now, just
place checks in your decoding sequence. Possible checks places, at first
sight, marked below:
line = arduino.readline().strip()
line = line.lstrip('{').rstrip('}').strip()
# check line not empty
# (actually big enough for at least {} + one key:val entry)
d = {}
# first get items in separate var and check how many:
for item in line.split(','):
item = item.strip() # not needed, for you strip key/val
again later
# first get tuple from split() and check its size is 2
key, value = item.split(':')
key = key.strip()
value = value.strip()# not needed, for int() itself strips
#
Re: [Tutor] Loop over floating point values
On Sun, Dec 1, 2013 at 7:26 PM, Steven D'Aprano st...@pearwood.info wrote:
On Sun, Dec 01, 2013 at 07:03:15PM +1000, Amit Saha wrote:
Hello,
Much to my disbelief, I realized I hadn't written a program in Python
as far as I can recall which required me to do something like this, in
psuedocode:
x = 0.1
for i = 0 to x step 0.01
# do something with i
end i
Such floating point loops are tricky to get right, thanks to rounding of
floats. Observe:
py x = 0.0
py while x 1.0:
... x += 0.1
...
py x == 1.0
False
py x
1.0999
We expect that after the loop is done, x should equal 1, but it doesn't.
That means that it actually loops one time too many.
Indeed, that's a good point. Surprisingly, C does it just fine:
# include stdio.h
int main(int argc, char **argv)
{
float x = 0.0;
while(x1)
{
x += 0.1;
printf(%f\n, x);
}
return 0;
}
gives the following output:
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
One way to fix this is to iterate over integers, and then divide just
before doing the work:
for x in range(0, 10):
print x/10.0
Yes, that's one approach to ensure that we do not exceed the hard limit of 1.
Another way is to use the recipes I have here:
http://code.activestate.com/recipes/577878-generate-equally-spaced-floats/
http://code.activestate.com/recipes/577881-equally-spaced-floats-part-2/
http://code.activestate.com/recipes/577068-floating-point-range/
I encourage you to read all three. If you have any questions, please
feel free to ask.
Thanks for sharing these, I will go through them.
Best,
Amit.
--
http://echorand.me
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Re: [Tutor] Loop over floating point values
On Sun, Dec 1, 2013 at 7:14 PM, Dominik George n...@naturalnet.de wrote: Hi, - Do not create a list of the floating point values as i=[0.01, 0.02, 0.03..] - either like that or by using a suitable mathematical formula combined with a list comprehension You could simply write your own version of xrange that does it, as a generator: def xrange_f(start, stop, step): x = start while x stop: yield x x += step Then, in your code, you can do: for f in xrange_f(0, 10, 0.01): pass Thanks Dominik. Yes, this is a good abstraction if I need this functionality at multiple places. Best, Amit. -- http://echorand.me ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Loop over floating point values
On Sun, Dec 1, 2013 at 7:47 PM, spir denis.s...@gmail.com wrote: On 12/01/2013 10:03 AM, Amit Saha wrote: Hello, Much to my disbelief, I realized I hadn't written a program in Python as far as I can recall which required me to do something like this, in psuedocode: x = 0.1 for i = 0 to x step 0.01 # do something with i end i Simply stated, I want to start from say a value, 0 and go upto 0.1 in increments of 0.01. I don't want to create a list with the values hard-coded and then iterate over it, and hence I would use a while loop instead: x = 0.1 while i x: # do something with i i += 0.01 I think this is one case, where you definitely cannot do this with a for loop assuming the following restrictions: - Do not create a list of the floating point values as i=[0.01, 0.02, 0.03..] - either like that or by using a suitable mathematical formula combined with a list comprehension - Use numpy's linspace() to create the list for you Thoughts? There is a general solution for this (a typical school problem ;-), maybe the reason why we rarely meet it in practice!). Depends on what your practice is. This will come up in any problem where you need a continuous stream of numbers. Like, drawing a circle with x=rcos(theta) and y=rsin(theta) with theta between 0 to 360. However, watch the issues with binary floats mentionned by Steven. # loop from x0 to x1 with step dx, total n passes x0, x1, dx, n = -0.3, 0.8, 0.2, 6 for i in range(n): x = x0 + dx * i print(x) Yes, IIUC, I think this is an easier problem considering that you care abut the number of passes here more than you care about the upper bound of the numbers. Thanks for sharing. Best, Amit. -- http://echorand.me ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Loop over floating point values
On Mon, Dec 2, 2013 at 4:36 PM, Asokan Pichai paso...@talentsprint.com wrote:
On Mon, Dec 2, 2013 at 11:58 AM, Amit Saha amitsaha...@gmail.com wrote:
On Sun, Dec 1, 2013 at 7:26 PM, Steven D'Aprano st...@pearwood.info
wrote:
On Sun, Dec 01, 2013 at 07:03:15PM +1000, Amit Saha wrote:
Hello,
Much to my disbelief, I realized I hadn't written a program in Python
as far as I can recall which required me to do something like this, in
psuedocode:
x = 0.1
for i = 0 to x step 0.01
# do something with i
end i
Such floating point loops are tricky to get right, thanks to rounding of
floats. Observe:
py x = 0.0
py while x 1.0:
... x += 0.1
...
py x == 1.0
False
py x
1.0999
We expect that after the loop is done, x should equal 1, but it doesn't.
That means that it actually loops one time too many.
Indeed, that's a good point. Surprisingly, C does it just fine:
I am not sure.
# include stdio.h
int main(int argc, char **argv)
{
float x = 0.0;
while(x1)
{
x += 0.1;
printf(%f\n, x);
}
return 0;
}
gives the following output:
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
Try double here instead of float.
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1.10
is what I get on a debian machine with gcc 4.8.2 , though I suspect that
these are not relevant.
Yes, I didn't mean to imply C's result as something which is
absolutely the case always. I believe, the inherent nature of floating
point number representations will make this an issue, always.
Best,
-Amit.
--
http://echorand.me
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Re: [Tutor] Loop over floating point values
On Mon, Dec 2, 2013 at 1:28 AM, Amit Saha amitsaha...@gmail.com wrote:
Indeed, that's a good point. Surprisingly, C does it just fine:
# include stdio.h
int main(int argc, char **argv)
{
float x = 0.0;
while(x1)
{
x += 0.1;
printf(%f\n, x);
}
return 0;
}
Python uses double precision:
import os, ctypes
open('tmp.c', 'w').write(r'''
... double test_d() {
... double x = 0.0;
... while (x 1.0)
... x += 0.1;
... return x;
... }
... float test_f() {
... float x = 0.0;
... while (x 1.0)
... x += 0.1;
... return x;
... }
... ''')
rc = os.system('gcc -shared -o tmp.so tmp.c')
tmp = ctypes.CDLL('./tmp.so')
tmp.test_d.restype = ctypes.c_double
tmp.test_f.restype = ctypes.c_float
tmp.test_d()
1.0999
tmp.test_f()
1.001192092896
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Re: [Tutor] Hash map and dictionaries
On Sun, Dec 1, 2013 at 7:40 AM, Reuben reuben.dl...@gmail.com wrote: Hi Question 1: - I would like to know the concept of hash map. Additionally, I got to know that hash maps are equivalent to dictionaries in python. I would like to understand the relationship between dictionaries and hash map better. Hash maps are a class of data structures which associate values with keys. They exhibit constant time average case behavior if every possible key is equally likely. They usually have O(n) worst case behavior. Python dictionaries are an implementation of hash maps using a particular choice of algorithms. Question 2: -- It is also said that in a list of may be 10,000 elements(specifically integers), hash maps would be a better option to find the occurrence of repetitive integers How can this be implemented using dictionaries for a list of 10,000 integer elements? You would use sets, not dictionaries. x = set(range(HUGE_NUM)) # 1 in x is as fast as -1 in x x = list(range(HUGE_NUM)) # 1 in x is much faster than -1 in x Sets use hash tables internally too, but they don't associate a value with the keys. They just mark whether or not the key is present. -- Devin ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
