Re: [Tutor] python-files
On 27/01/2019 14:57, Asad wrote:
> print("first:", args.first)
> print("second:", args.second)
>
> When I execute the script it gives error :
>
> python python_json_20001_oratest_v1.py "file1"
> ('first:', 'file1')
> ('second:', None)
Note that the second file is None.
> Traceback (most recent call last):
> File "test.py", line 211, in
> with open(args.second, 'r') as f :
> TypeError: coercing to Unicode: need string or buffer, NoneType found
Note that you get a TypeError because you passed None instead
of a valid filename.
> try :
> with open(args.second, 'r') as f :
> for line in f:
> print line
> except IOError:
> print "The default error is err-1 because file2 was not provided "
Note that you are trying to catch an IOError but you are getting a
TypeError. You need to add another except clause for the TypeError.
Or test for a None second file value at the start of your code...
> Does that mean my try and except block is not working because if
> args.second is None as in this case then it should print "The default
> error is err-1 because file2 was not provided "
It is working. You just aren't catching the correct error type.
It will only type the message you've given if you get an
IOError, but the open() code isn't getting that far,
it's failing on the parameter type.
> Please advice ,
OK, I advise you to delete the text below where you no longer
need it. Some users pay by the byte and all this excess text
costs them money. More than 75% of your message is included
text that we have already seen.
> Thanks,
>
>
>> -- Forwarded message --
>> From: Peter Otten <__pete...@web.de>
>> To: tutor@python.org
...
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
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Re: [Tutor] python-files
Asad wrote:
> Hi All ,
>
> I tried the following code :
>
> parser = argparse.ArgumentParser()
> parser.add_argument("first")
> parser.add_argument("second", nargs="?")
> args = parser.parse_args()
> print("first:", args.first)
>
> print("second:", args.second)
>
> When I execute the script it gives error :
>
> python python_json_20001_oratest_v1.py "file1"
> ('first:', 'file1')
> ('second:', None)
> Traceback (most recent call last):
> File "test.py", line 211, in
> with open(args.second, 'r') as f :
> TypeError: coercing to Unicode: need string or buffer, NoneType found
>
>
> if I see in line number 211 it with open(args.second, 'r') as f :
>
> try :
> with open(args.second, 'r') as f :
> for line in f:
> print line
> except IOError:
> print "The default error is err-1 because file2 was not provided
> "
How do you know that the file was not provided? The name might have been
misspelt or the user lacks the permission to read it.
> Does that mean my try and except block is not working because if
> args.second is None as in this case then it should print "The default
> error is err-1 because file2 was not provided "
>
> Please advice ,
If you just want to terminate the script with a helpful message you should
make the second argument mandatory, too:
parser = argparse.ArgumentParser()
parser.add_argument("first")
parser.add_argument("second")
args = parser.parse_args()
That way the parse_args() call will terminate the script and the user will
see an error message immediately.
If for some reason you want to keep the argument optional you can check for
None before trying to open the file:
if args.second is not None:
try:
with open(args.second, 'r') as f :
for line in f:
print line
except IOError as err:
print err # print actually what happened, not what you guess
else:
print "File 'second' was not provided on the command line"
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Re: [Tutor] python-files
Hi All ,
I tried the following code :
parser = argparse.ArgumentParser()
parser.add_argument("first")
parser.add_argument("second", nargs="?")
args = parser.parse_args()
print("first:", args.first)
print("second:", args.second)
When I execute the script it gives error :
python python_json_20001_oratest_v1.py "file1"
('first:', 'file1')
('second:', None)
Traceback (most recent call last):
File "test.py", line 211, in
with open(args.second, 'r') as f :
TypeError: coercing to Unicode: need string or buffer, NoneType found
if I see in line number 211 it with open(args.second, 'r') as f :
try :
with open(args.second, 'r') as f :
for line in f:
print line
except IOError:
print "The default error is err-1 because file2 was not provided "
Does that mean my try and except block is not working because if
args.second is None as in this case then it should print "The default
error is err-1 because file2 was not provided "
Please advice ,
Thanks,
> -- Forwarded message --
> From: Peter Otten <__pete...@web.de>
> To: tutor@python.org
> Cc:
> Bcc:
> Date: Sun, 27 Jan 2019 10:30:12 +0100
> Subject: Re: [Tutor] python - files
> Cameron Simpson wrote:
>
> > Mats has mentioned the modules getopt and argparse etc. These are
> > primarily aimed at option parsing ("-v", "-o foo"). Your situation
> > occurs _after_ the option parsing (in your case, there are no options).
>
> Not argparse. The main advantage over optparse is its handling of
> positional
> arguments. Your custom logic
>
> > def main(argv):
> > cmd = argv.pop(0) # collect the command word
> > badopts = False
> > # mandatory first argument
> > if not argv:
> > print("%s: missing first argument" % cmd, file=sys.stderr)
> > badopts = True
> > else:
> > first = argv.pop(0)
> > # optional second argument
> > if argv:
> > second = argv.pop(0)# explicit argument 2, use it
> > else:
> > second = None # or some otherdefault
> > if argv:
> > print("%s: extra arguments: %r" % (cmd, argv), file=sys.stderr)
> > badopts = true
> > if badopts:
> > print("%s: invalid invocation, aborting" % cmd, file=sys.stderr)
> > return 2
> > ... work with first and second ...
>
> can roughly be replicated with the two lines
>
> parser.add_argument("first")
> parser.add_argument("second", nargs="?")
>
> A working script:
>
> $ cat test.py
> #!/usr/bin/python3
> import argparse
>
> def main():
> parser = argparse.ArgumentParser()
>
> parser.add_argument("first")
> parser.add_argument("second", nargs="?")
>
> args = parser.parse_args()
>
> print("first:", args.first)
> print("second:", args.second)
>
> if __name__ == "__main__":
> main()
>
> $ ./test.py
> usage: test.py [-h] first [second]
> test.py: error: the following arguments are required: first
>
> $ ./test.py -h
> usage: test.py [-h] first [second]
>
> positional arguments:
> first
> second
>
> optional arguments:
> -h, --help show this help message and exit
>
> $ ./test.py ONE
> first: ONE
> second: None
>
> $ ./test.py ONE TWO
> first: ONE
> second: TWO
>
> $ ./test.py ONE TWO THREE
> usage: test.py [-h] first [second]
> test.py: error: unrecognized arguments: THREE
>
> Argparse makes a usable standard command line interface easy to set up (if
> you need non-standard behaviour it gets a bit harder).
>
> There is also a companion module argcomplete (not in the stdlib) that
> enables autocompletion.
>
>
>
>
>
>
> -- Forwarded message --
> From: Cameron Simpson
> To: tutor@python.org
> Cc:
> Bcc:
> Date: Sun, 27 Jan 2019 20:54:13 +1100
> Subject: Re: [Tutor] python - files
> On 27Jan2019 10:30, Peter Otten <__pete...@web.de> wrote:
> >Cameron Simpson wrote:
> >> Mats has mentioned the modules getopt and argparse etc. These are
> >> primarily aimed at option parsing ("-v", "-o foo"). Your situation
> >> occurs _after_ the option parsing (in your case, there are no options).
> >
> >Not argparse. The main advantage over optparse is its handling of
> positional
> >arguments.
>
> I stand corrected.
>
> >Your custom logic
> [...]
> &g
Re: [Tutor] python - files
On 27Jan2019 10:30, Peter Otten <__pete...@web.de> wrote:
Cameron Simpson wrote:
Mats has mentioned the modules getopt and argparse etc. These are
primarily aimed at option parsing ("-v", "-o foo"). Your situation
occurs _after_ the option parsing (in your case, there are no options).
Not argparse. The main advantage over optparse is its handling of positional
arguments.
I stand corrected.
Your custom logic
[...]
can roughly be replicated with the two lines
parser.add_argument("first")
parser.add_argument("second", nargs="?")
[... extended example ...]
Thank you!
Cheers,
Cameron Simpson
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Re: [Tutor] python - files
Cameron Simpson wrote:
> Mats has mentioned the modules getopt and argparse etc. These are
> primarily aimed at option parsing ("-v", "-o foo"). Your situation
> occurs _after_ the option parsing (in your case, there are no options).
Not argparse. The main advantage over optparse is its handling of positional
arguments. Your custom logic
> def main(argv):
> cmd = argv.pop(0) # collect the command word
> badopts = False
> # mandatory first argument
> if not argv:
> print("%s: missing first argument" % cmd, file=sys.stderr)
> badopts = True
> else:
> first = argv.pop(0)
> # optional second argument
> if argv:
> second = argv.pop(0)# explicit argument 2, use it
> else:
> second = None # or some otherdefault
> if argv:
> print("%s: extra arguments: %r" % (cmd, argv), file=sys.stderr)
> badopts = true
> if badopts:
> print("%s: invalid invocation, aborting" % cmd, file=sys.stderr)
> return 2
> ... work with first and second ...
can roughly be replicated with the two lines
parser.add_argument("first")
parser.add_argument("second", nargs="?")
A working script:
$ cat test.py
#!/usr/bin/python3
import argparse
def main():
parser = argparse.ArgumentParser()
parser.add_argument("first")
parser.add_argument("second", nargs="?")
args = parser.parse_args()
print("first:", args.first)
print("second:", args.second)
if __name__ == "__main__":
main()
$ ./test.py
usage: test.py [-h] first [second]
test.py: error: the following arguments are required: first
$ ./test.py -h
usage: test.py [-h] first [second]
positional arguments:
first
second
optional arguments:
-h, --help show this help message and exit
$ ./test.py ONE
first: ONE
second: None
$ ./test.py ONE TWO
first: ONE
second: TWO
$ ./test.py ONE TWO THREE
usage: test.py [-h] first [second]
test.py: error: unrecognized arguments: THREE
Argparse makes a usable standard command line interface easy to set up (if
you need non-standard behaviour it gets a bit harder).
There is also a companion module argcomplete (not in the stdlib) that
enables autocompletion.
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Re: [Tutor] python - files
Mats has mentioned the modules getopt and argparse etc. These are
primarily aimed at option parsing ("-v", "-o foo"). Your situation
occurs _after_ the option parsing (in your case, there are no options).
Alan has talked about explicitly checking the length of sys.argv, much
as you are doing, or accessing the (missing) argument and catching an
exception.
There's a middle ground, which is a little more flexible, which is to
_consume_ the command line arguments. The argv array is a list, and can
be modified. So:
def main(argv):
cmd = argv.pop(0) # collect the command word
badopts = False
# mandatory first argument
if not argv:
print("%s: missing first argument" % cmd, file=sys.stderr)
badopts = True
else:
first = argv.pop(0)
# optional second argument
if argv:
second = argv.pop(0)# explicit argument 2, use it
else:
second = None # or some otherdefault
if argv:
print("%s: extra arguments: %r" % (cmd, argv), file=sys.stderr)
badopts = true
if badopts:
print("%s: invalid invocation, aborting" % cmd, file=sys.stderr)
return 2
... work with first and second ...
You can see here that we process the arguments from left to right,
consuming the valid ones as we find them, and setting a flag for
incorrect arguments. At the end we test the flag and abort if it is set.
otherwise we process knowing we have valid values.
One important aspect of the above code is that you do not wire in an
explicit length for sys.argv such as 2 or 3. That way you can easily
change your code later if you want more arguments without running around
adjusting such fixed numbers.
The other important aspect is usability: the above code complains about
each issue it encounters, and finally quits with an additional message.
In a real programme that addition message would include a "usage"
message which describes the expected arguments.
Cheers,
Cameron Simpson
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Re: [Tutor] python - files
On 1/26/19 1:20 AM, Asad wrote: > Hi All , > >I would like to know how do I make and option file as an argument on > command propmnt in python I don't know your context for asking this question. Alan has already explained what you need to do for your issue, and whatever your needs it is certainly worthwhile to understand how sys.argv works. Just wanted to add, you find yourself having a need for processing a non-trivial amount of arguments, this is a problem that is well addressed in the Python community... the standard library now has three modules for that - the "original" (UNIX/POSIX like) getopt module, the currently preferred argparse module, and the optparse module it replaced (which is now considered deprecated), as well as several very good modules which are not in the standard library like docopt and click (just naming two as examples, not endorsing anything). So you don't need to reinvent the wheel here if you have heavy duty needs - spend your time on other parts of the problems you are solving. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] python - files
On 26/01/2019 08:20, Asad wrote: >At present I using : > > if len(sys.argv) == 3: > first = sys.argv[1] > second = sys.argv[2] > else: > print "enter the second argument" > It works well for the following command : > python test.py file1 file2 Correct because it tests if there are 2 arguments passed > However I have another case where only file1 may be present so file1 is > mandatory for this script to run however file2 is optionnal : > > if len(sys.argv) == 2: > first_log = sys.argv[1] > second_log = sys.argv[2] But this will always give an error because you test for only one argument but then try to read two! It will always give an error. > It gives error : > >second_log = sys.argv[2] > IndexError: list index out of range > > > How do I acheive this because if python test.py file1 file2 then I would > process both files . You need to check how many arguments are passed. if len(sys.argv) == 2: # read one argument elif len(sys.argv) == 3: # read 2 arguments elif ... etc You could alternatively use exception handling to catch the IndexError but I think the explicit test in this case more clearly shows what you are intending. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.amazon.com/author/alan_gauld Follow my photo-blog on Flickr at: http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] python - files
Hi All , I would like to know how do I make and option file as an argument on command propmnt in python . At present I using : if len(sys.argv) == 3: first = sys.argv[1] second = sys.argv[2] else: print "enter the second argument" It works well for the following command : python test.py file1 file2 However I have another case where only file1 may be present so file1 is mandatory for this script to run however file2 is optionnal : if len(sys.argv) == 2: first_log = sys.argv[1] second_log = sys.argv[2] pthon test.py file1 It gives error : second_log = sys.argv[2] IndexError: list index out of range How do I acheive this because if python test.py file1 file2 then I would process both files . If python test.py file1 is given then I would process file1 using the variable first_log . Please advice . Thanks, ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
