[docs] [issue32573] sys.argv documentation should include caveat for embedded environments

[Pedro]

New submission from Pedro <pgacv2+pythonbugs at gmail.com>:

Embedded Python interpreters, such as Boost.Python, do not have sys.argv available. (sys itself works fine.) This causes the interpreter to crash with the following exception when you try to access argv:

    AttributeError: 'module' object has no attribute 'argv'

I'm not sure how closely related this is to #15577 or PEP 432. A simple workaround is to manually assign a list with an empty string to argv, as suggested by https://github.com/google/oauth2client/issues/642. However, the documentation for the sys module makes no mention of this special case for argv, and the line at the top that says "It is always available" can easily be interpreted to mean that *all* of sys's attributes will always be available. I suggest adding the following to the documentation for sys.argv:

========

Since `argv` contains the list of **command line** arguments passed to the Python interpreter, `argv` is not available within embedded interpreters, and scripts that run in embedded environments will raise an `AttributeError` when they attempt to access `argv`. As a workaround, assign a list with an empty string manually:
```
import sys

if not hasattr(sys, 'argv'):
    sys.argv  = ['']
```

----------
assignee: docs at python
components: Documentation
messages: 310105
nosy: docs at python, pgacv2
priority: normal
severity: normal
status: open
title: sys.argv documentation should include caveat for embedded environments
type: enhancement
versions: Python 2.7, Python 3.4, Python 3.5, Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32573>
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