python file operation

Question

please, what is the meaning of this line:

return [f[:f.rindex(".")] for f in os.listdir(path) if f and len(f) >= 4 and f[-2:] 

== "py" and f[-1] != "o" and f[-1] != "c"]

I found it in a script in this link :

http://www-users.cs.umn.edu/~mein/blender/plugins/python/misc/scriptloader/TheOneScript.py

I know that i needed to split the file name from its extenstion (.py) .. but why len(f)>=4

and what about f[-1] != "o" or "c" .. what this is mean ?

Answer 1

I'd suggest

[f[:-3] for f in glob.iglob("*.py")]

as a concise alternative to the given code.

Answer 2

The length check is because the shortest sensible filename is a single character followed by .py, which gives at least 4 characters.

The last checks seem to be trying to ingore the compiled files with extensions .pyc and .pyo, but it's totally unnecessary as they won't match the condition f[-2:] == "py".

For splitting a filename into a root and extension you can also consider using os.path.splitext.

[root for (root, ext) in map(os.path.splitext, os.listdir(path)) if ext == '.py']

Answer 3

This line returns all files in a directory which are at least 4 characters long, do not end with o or c but end with py. It cuts the remainer from the files, so blubber.py will be converted to blubber. I suggest the following solution:

[x[:-3] for x in os.listdir('.') if x.endswith(".py")]

Answer 4

f[-1] is the last element in the iterable, in this case, the last letter of f

This would probably be clearer:

[name for name, ext in [f.rsplit('.', 1) for f in os.listdir('.')] if ext == 'py']