CODEWITHSUNDEEP
pythoncompilation
udaya
udaya

Reputation: 77

Python file compilation and distinguish, how this happens

While going through many concepts, this comes to my min (it may be silly). Please advise me how following scenario being achieved

Say in a folder I have "z.pyc" file (no z.py).

Now I created z.py at the same location.

As per my understanding first time execution of z.py will update z.pyc , so from second time trial z.py and z.pyc should give same result.

But it is not happening. z.py and z.pyc are giving distinguish results every time. Please suggest how this scenario being achieved.

Upvotes: 0

Views: 38

Answers (1)

Robᵩ
Robᵩ

Reputation: 168706

"first time execution of z.py will update z.pyc"

No, "execution of z.py" will never create, update, nor reference, z.py. Only an import z statement will create or make use of z.pyc.

1) .pyc files are created when one performs an import of a file, never when run executes a file.

2) import z will refresh the compiled version, if required.

3) Running python z.pyc will always run the compiled version of the file, whereas python z.py will never run the compiled version of the file.

So, one sequence of events that might lead to the confusing results above is:

$ echo "print 'first file'" > z.py
$ echo "import z" > main.py
$ python main.py
first file
$ echo "print 'second file'" > z.py
$ python z.py
second file
$ python z.pyc
first file

The lesson to learn? Never run python z.pyc, always run python z.py.

Upvotes: 2

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