Difference between file and sys.argv[0]

Question

Is there any difference between:

__file__

and

sys.argv[0]

Because both seem to be doing the same thing: they hold the name of the script.

If there is no difference, then why is it that __file__ is used in almost all someplaces whereas I have never seen sys.argv[0] being used.

score 26 · Accepted Answer · answered May 01 '11 at 21:41

26

__file__ is the name of the current file, which may be different from the main script if you are inside a module or if you start a script using execfile() rather than by invoking python scriptname.py. __file__ is generally your safer bet.

answered May 01 '11 at 21:41

Sven Marnach

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sys.argv[0] may even be a module name rather than a file name if your script was executed with the `-m` switch, or a directory or zipfile name if you are using bundled execution. – ncoghlan May 02 '11 at 13:14
Isn't \__file\__ supposed to be private and therefore not queried directly? – Bitcoin Cash - ADA enthusiast May 15 '17 at 00:30
1

@Tiago No, it's fine to access it directly. See e.g. http://stackoverflow.com/a/8689983/279627. – Sven Marnach May 15 '17 at 14:46

score 7 · Answer 2 · edited May 01 '11 at 23:19

7

It's only the same if you are in the "main" script of your python programm. If you import other files, __file__ will contain the path to that file, but sys.argv will still hold the same values.

edited May 01 '11 at 23:19

tzot

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answered May 01 '11 at 21:42

Achim

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Lumi · Answer 3 · 2011-05-01T23:24:59.850

3

It's like Sven said.

MiLu@Dago: /tmp > cat file.py
import sys
import blub
print __file__
print sys.argv[0]

MiLu@Dago: /tmp > cat blub.py
import sys
print "BLUB: " + __file__
print "BLUB: " + sys.argv[0]

MiLu@Dago: /tmp > python file.py
BLUB: /tmp/blub.pyc
BLUB: file.py
file.py
file.py

I thought that __file__ was replaced with the filename during a preprocessor step. I was not 100 % sure that's actually the case in Python - but it is in C/C++ and Perl. In Python, this might be different as the __file__ is also correct for compiled Python files (pyc), and there doesn't seem to be any trace of the filename in that file's contents.

edited May 01 '11 at 23:24

answered May 01 '11 at 21:56

Lumi

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Ludwig: Probably you should do some more experimentation. Create an empty file named `empty.py`. At the Python interactive prompt, enter this line: `import empty; print(empty.__file__); reload(empty); print(empty.__file__)` ... then edit your answer. – John Machin May 01 '11 at 22:48
Ludwig: Facts: `__file__` is an attribute of the module, created automatically when the module is loaded. CPython doesn't have a preprocessor step. – John Machin May 01 '11 at 23:46

score 0 · Answer 4 · answered May 01 '11 at 21:43

0

Actually argv[0] might be a script name or a full path to the script + script name, depending on the os.

Here's the entry in official documentation http://docs.python.org/py3k/library/sys.html#sys.argv

answered May 01 '11 at 21:43

Stanislav Ageev

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Difference between file and sys.argv[0]

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Difference between __file__ and sys.argv[0]

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Difference between file and sys.argv[0]