[issue10523] argparse has problem parsing option files containing empty rows

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
type: crash -> behavior

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[issue10523] argparse has problem parsing option files containing empty rows

[paul j3]

Changes by paul j3 :


--
nosy: +paul.j3

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[issue10523] argparse has problem parsing option files containing empty rows

[Caelyn McAulay]

Caelyn McAulay added the comment:

I've attached a patch making the changes I suggested, assuming that the current 
behaviour is desirable. It documents the behaviour of argparse on files with 
blank lines and changes the way the error message that argparse generates when 
encountering unrecognized arguments is generated.

When a blank line is included at the end of a file, the resulting error message 
is now: "argparse_example.py: error: unrecognized arguments: ''". This also 
makes it obvious when the problem is white space, e.g. if an argument has 
trailing spaces, this also makes that obvious.

--
keywords: +patch
Added file: http://bugs.python.org/file34875/argparse_blanklines.patch

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[issue10523] argparse has problem parsing option files containing empty rows

[Caelyn McAulay]

Caelyn McAulay added the comment:

The current behaviour takes empty lines and interprets them as empty strings. 

The attached demonstration script shows the error occurring. The first case is 
a simple example to illustrate what happens in the general case. The second 
case shows empty lines being interpreted as empty strings and assigned to 
arguments.

The third case, despite being very similar to the first, results in argparse 
exiting with an error message. Internally, what is happening is, after taking 
the 'foo' and 'baz' arguments and assigning them 'bar' and 'quux' respectively, 
it reads in an argument "", which it does not recognize. And produces the 
following error message:

"argparse_example.py: error: unrecognized arguments:"

The error message, in it's current form, is kind of opaque.

For the third case, if we move the blank line to between 'bar' and '-baz', the 
same error results, as again it tried to interpret the blank line as an 
argument. If we move the blank line to the start of the file, same thing again. 

If we move the blank line between '-foo' and 'bar', instead the error reads: 
"argparse_example.py: error: unrecognized arguments: bar" - which is at least 
somewhat comprehensible.

The question is, how should blank lines be handled? 

Should they be accepted as possible values for arguments? 

If they fall into spaces where arguments (versus values for arguments) are 
expected, should we skip them?

If the current handling is fine, I would propose updating the documentation to 
add the following after the paragraph that begins "Arguments read from a file 
...":

"By default, blank lines are interpreted as empty strings. An empty string is 
not an acceptable argument; but it is an acceptable value for an argument."

And changing the way that the error from argparse is displayed so that it is 
more obvious what "argparse_example.py: error: unrecognized arguments:" means.

--
nosy: +math_foo
Added file: http://bugs.python.org/file34860/argparse_example.py

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[issue10523] argparse has problem parsing option files containing empty rows

[Steven Bethard]

Steven Bethard  added the comment:

Crashing on an empty line is definitely a bug.

Each line being a single option is documented behavior:

http://docs.python.org/dev/library/argparse.html#fromfile-prefix-chars

--
nosy: +bethard

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[issue10523] argparse has problem parsing option files containing empty rows

[Michal Pomorski]

Changes by Michal Pomorski :


--
type:  -> crash

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[issue10523] argparse has problem parsing option files containing empty rows

[Michal Pomorski]

New submission from Michal Pomorski :

When using the argument file option, i.e  @file_with_arguments the following 
problems arise:

1. argparse crashes when the file contains an empty line (even if it is the 
last line) - arg_string[0] is done when arg_string is empty. 
This is caused by the use of splitlines() instead of strip().split() in the 
function _read_args_from_files(self, arg_strings)

2. options separated by spaces in one row are passed as a single long option, 
meaning each option has to be on its own line.
This is caused by the new function 
   def convert_arg_line_to_args(self, arg_line):
return [arg_line]
   which should be 
return arg_line.split()


Both problems are caused by a modification in
def _read_args_from_files(self, arg_strings)
The version from argparse 1.0.1 worked well and was correct, it should be 
sufficient to reverse the changes done from 1.0.1 to 1.1.

Here is the old implementation:

def _read_args_from_files(self, arg_strings):
# expand arguments referencing files
new_arg_strings = []
for arg_string in arg_strings:

# for regular arguments, just add them back into the list
if arg_string[0] not in self.fromfile_prefix_chars:
new_arg_strings.append(arg_string)

# replace arguments referencing files with the file content
else:
try:
args_file = open(arg_string[1:])
try:
arg_strings = args_file.read().strip().split()
arg_strings = self._read_args_from_files(arg_strings)

new_arg_strings.extend(arg_strings)
finally:
args_file.close()
except IOError:
err = _sys.exc_info()[1]
self.error(str(err))

# return the modified argument list
return new_arg_strings

--
components: Library (Lib)
messages: 122314
nosy: Michal.Pomorski
priority: normal
severity: normal
status: open
title: argparse has problem parsing option files containing empty rows
versions: Python 2.7

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