[Tutor] Print record x in a file
Kent, Yes you are right. I looked at your code and that makes sense now. Thanks for explaining that. ALL-NEW Yahoo! Messenger - all new features - even more fun! ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Print record x in a file
Max Noel wrote: On Jan 23, 2005, at 22:08, Liam Clarke wrote: Don't you mean x=random.randint(0, lenoflist) ?? I'm assuming you want an integer. random.randrange() returns an item (which can be a float or whatever, but by default is an int) in the specified range. In that case, an int between 0 and lenoflist. The advantage over random.randint is that you can specify a step. Thus, random.randrange(0, 257, 2) will return an even number between 0 and 256 inclusive. Also the output of randint() is inclusive of both endpoints - with the above statement you will have 0 <= x <= lenoflist. So in that case you would want lenoflist = len(listcontents) - 1 Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Print record x in a file
On Jan 23, 2005, at 22:08, Liam Clarke wrote:
Don't you mean
x=random.randint(0, lenoflist) ?? I'm assuming you want an integer.
random.randrange() returns an item (which can be a float or whatever,
but by default is an int) in the specified range. In that case, an int
between 0 and lenoflist.
The advantage over random.randint is that you can specify a step. Thus,
random.randrange(0, 257, 2) will return an even number between 0 and
256 inclusive.
While although this code below does work many times
nothing is printed out.
import random
i = 0
while i < 10:
file = open('test.rantxt')
listcontents = file.readlines()
file.close()
lenoflist = len(listcontents)#-1
x = random.randrange(0,lenoflist)
print listcontents[x], i
i = i +1
Anyway, the problem with this function is that len returns a number of
items, but Python, like most good programming languages (and
mathematicians), counts starting from 0. Thus, the first element in a
list is foo[0].
foo[len(foo)] will raise an IndexError.
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Re: [Tutor] Print record x in a file
Don't you mean
x=random.randint(0, lenoflist) ?? I'm assuming you want an integer.
On Sun, 23 Jan 2005 21:55:27 + (GMT), David Holland
<[EMAIL PROTECTED]> wrote:
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> >1. Re: Print record x in a file (Kent Johnson)
> >2. How would python messure up in performance?
> > (Kevin)
> >3. Re: How would python messure up in
> > performance? (Max Noel)
> >4. Re: Print record x in a file (David Holland)
> >5. on the way to find pi (Ali Polatel)
> >6. Re: on the way to find pi (Max Noel)
> >7. Re: on the way to find pi (Orri Ganel)
> >
> >
> >
> --
> >
> > Message: 1
> > Date: Sun, 23 Jan 2005 07:46:08 -0500
> > From: Kent Johnson <[EMAIL PROTECTED]>
> > Subject: Re: [Tutor] Print record x in a file
> > Cc: tutor python
> > Message-ID: <[EMAIL PROTECTED]>
> > Content-Type: text/plain; charset=ISO-8859-1;
> > format=flowed
> >
> > Since len(listcontents) is one greater than the
> > largest valid index of listcontents, the correct
> > use of randrange() for this problem is
> >x = random.randrange(0, len(listcontents))
> >
>
>
> Kent,
>
> I know that you know far more about python than me but
> is that right ?
> I created file with 4 records and this code did print
> them all randomly:-
>
> import random
> i = 0
> while i < 10:
> file = open('filename')
> listcontents = file.readlines()
> file.close()
> lenoflist = len(listcontents)-1
> x = random.randrange(0,lenoflist)
> print listcontents[x], i
> i = i +1
>
> While although this code below does work many times
> nothing is printed out.
> import random
> i = 0
> while i < 10:
> file = open('test.rantxt')
> listcontents = file.readlines()
> file.close()
> lenoflist = len(listcontents)#-1
> x = random.randrange(0,lenoflist)
> print listcontents[x], i
> i = i +1
>
>
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[Tutor] Print record x in a file
--- [EMAIL PROTECTED] wrote:
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> visit
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> [EMAIL PROTECTED]
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> When replying, please edit your Subject line so it
> is more specific
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> Today's Topics:
>
>1. Re: Print record x in a file (Kent Johnson)
>2. How would python messure up in performance?
> (Kevin)
>3. Re: How would python messure up in
> performance? (Max Noel)
>4. Re: Print record x in a file (David Holland)
>5. on the way to find pi (Ali Polatel)
>6. Re: on the way to find pi (Max Noel)
>7. Re: on the way to find pi (Orri Ganel)
>
>
>
------
>
> Message: 1
> Date: Sun, 23 Jan 2005 07:46:08 -0500
> From: Kent Johnson <[EMAIL PROTECTED]>
> Subject: Re: [Tutor] Print record x in a file
> Cc: tutor python
> Message-ID: <[EMAIL PROTECTED]>
> Content-Type: text/plain; charset=ISO-8859-1;
> format=flowed
>
> Since len(listcontents) is one greater than the
> largest valid index of listcontents, the correct
> use of randrange() for this problem is
>x = random.randrange(0, len(listcontents))
>
Kent,
I know that you know far more about python than me but
is that right ?
I created file with 4 records and this code did print
them all randomly:-
import random
i = 0
while i < 10:
file = open('filename')
listcontents = file.readlines()
file.close()
lenoflist = len(listcontents)-1
x = random.randrange(0,lenoflist)
print listcontents[x], i
i = i +1
While although this code below does work many times
nothing is printed out.
import random
i = 0
while i < 10:
file = open('test.rantxt')
listcontents = file.readlines()
file.close()
lenoflist = len(listcontents)#-1
x = random.randrange(0,lenoflist)
print listcontents[x], i
i = i +1
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Re: [Tutor] Print record x in a file
--- "Jacob S." <[EMAIL PROTECTED]> wrote:
> > This will get a random record
> > I hope you do not think the comments are
> patronising
> > but you did say you are new so I did not want to
> give
> > naked code.
> >
> > import random
> > #the above gives the program the ability to get a
> > #pseudo random number
> > file = open('test.rantxt')
> > listcontents = file.readlines()
> > #gives you the file as a list of records or it did
> on
> > #(assuming each line is a record)
> > file.close()
> > lenoflist = len(listcontents)-1
> > #find the length of the list and take one of
> because
> > computers count from 0
>
> Yes, but len returns counting from 1.
> Anyway, you would have to add one to correct that
> anyway, wouldn't you?
As len(list) gives the length and when the elements of
the list are number for element 0 onwards, the last
element is number len(list) -1. Test yourself
anyway.
Randrange does gives an integer or it did when I
tested this as otherwise it would have errored.
I don't know if it always does, what do other people
think ?
However Kent's idea of random.choice(list) is better
than my idea as it is one less line of code !!
.
If you have a length of 5
> If randrange is start <= x *<=* end, then you don't
> have to add one, you
> just use the length.
> If randrange is start<= x < end like __builtin__
> range, you have to put
> randrange(1,lenoflist+1)
>
> > x = random.randrange(0,lenoflist)
>
> I would use randint because list indices need to be
> integers -- unless of
> course I mistaken and
> randrange returns an integer also. (But that would
> be repetitive to have to
> functions do the same thing)
>
> > print listcontents[x]
>
> HTH,
> Jacob
>
>
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Re: [Tutor] Print record x in a file
Jacob S. wrote:
import random
#the above gives the program the ability to get a
#pseudo random number
file = open('test.rantxt')
listcontents = file.readlines()
#gives you the file as a list of records or it did on
#(assuming each line is a record)
file.close()
lenoflist = len(listcontents)-1
#find the length of the list and take one of because
computers count from 0
Yes, but len returns counting from 1.
Anyway, you would have to add one to correct that anyway, wouldn't you?
If randrange is start <= x *<=* end, then you don't have to add one, you
just use the length.
If randrange is start<= x < end like __builtin__ range, you have to put
randrange(1,lenoflist+1)
x = random.randrange(0,lenoflist)
I would use randint because list indices need to be integers -- unless of
course I mistaken and
randrange returns an integer also. (But that would be repetitive to have to
functions do the same thing)
A quick check of the module docs (Jacob, do you know where to find the
docs?) gives
randrange( [start,] stop[, step])
Return a randomly selected element from range(start, stop, step). This is equivalent to
choice(range(start, stop, step)), but doesn't actually build a range object. New in version 1.5.2.
So the limits on randrange() are the same as for range() - it is start <= x < stop. And the returned
value is an integer.
Since len(listcontents) is one greater than the largest valid index of listcontents, the correct
use of randrange() for this problem is
x = random.randrange(0, len(listcontents))
print listcontents[x]
HTH,
Jacob
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Re: [Tutor] Print record x in a file
Jacob S. wrote:
This will get a random record
I hope you do not think the comments are patronising
but you did say you are new so I did not want to give
naked code.
import random
#the above gives the program the ability to get a
#pseudo random number
file = open('test.rantxt')
listcontents = file.readlines()
#gives you the file as a list of records or it did on
#(assuming each line is a record)
file.close()
lenoflist = len(listcontents)-1
#find the length of the list and take one of because
computers count from 0
Yes, but len returns counting from 1.
Anyway, you would have to add one to correct that anyway, wouldn't you?
If randrange is start <= x *<=* end, then you don't have to add one, you
just use the length.
If randrange is start<= x < end like __builtin__ range, you have to put
randrange(1,lenoflist+1)
x = random.randrange(0,lenoflist)
I would use randint because list indices need to be integers -- unless of
course I mistaken and
randrange returns an integer also. (But that would be repetitive to
have to
functions do the same thing)
print listcontents[x]
HTH,
Jacob
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How about random.choice() ? Ie:
>>> print random.choice(f.readlines())
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Re: [Tutor] Print record x in a file
This will get a random record
I hope you do not think the comments are patronising
but you did say you are new so I did not want to give
naked code.
import random
#the above gives the program the ability to get a
#pseudo random number
file = open('test.rantxt')
listcontents = file.readlines()
#gives you the file as a list of records or it did on
#(assuming each line is a record)
file.close()
lenoflist = len(listcontents)-1
#find the length of the list and take one of because
computers count from 0
Yes, but len returns counting from 1.
Anyway, you would have to add one to correct that anyway, wouldn't you?
If randrange is start <= x *<=* end, then you don't have to add one, you
just use the length.
If randrange is start<= x < end like __builtin__ range, you have to put
randrange(1,lenoflist+1)
x = random.randrange(0,lenoflist)
I would use randint because list indices need to be integers -- unless of
course I mistaken and
randrange returns an integer also. (But that would be repetitive to have to
functions do the same thing)
print listcontents[x]
HTH,
Jacob
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[Tutor] Print record x in a file
This will get a random record
I hope you do not think the comments are patronising
but you did say you are new so I did not want to give
naked code.
import random
#the above gives the program the ability to get a
#pseudo random number
file = open('test.rantxt')
listcontents = file.readlines()
#gives you the file as a list of records or it did on
#(assuming each line is a record)
file.close()
lenoflist = len(listcontents)-1
#find the length of the list and take one of because
computers count from 0
x = random.randrange(0,lenoflist)
print listcontents[x]
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