问题
I'm trying to do this:
import os
[x for x in os.listdir('.') if os.path.isfile(x)]
[x for x in os.listdir('dirname') if os.path.isfile(x)]
[x for x in os.listdir(os.path.abspath('dirname')) if os.path.isfile(os.path.abspath(x))]
The first line works:
[x for x in os.listdir('.') if os.path.isfile(x)]
But the next two:
[x for x in os.listdir('dirname') if os.path.isfile(x)]
and
[x for x in os.listdir(os.path.abspath('dirname')) if os.path.isfile(os.path.abspath(x))]
just output []
Why?
回答1:
Because you need to join the dirname with x , os.listdir() just lists the contents directly, the contents do not have full path.
Example -
[x for x in os.listdir('dirname') if os.path.isfile(os.path.join('dirname',x))]
When the full path is not given, os.path.isfile() searches in the current directory, hence when you give '.' to os.listdir() you get a correct list back.
Example -
Lets say some folder - /a/b/c - has files - x and y in it.
when you do - os.listdir('/a/b/c') , the list returned looks like -
['x','y']
Even if you give absolute path inside os.listdir() , the files returned in the list would have relative path to the dir. You would manually need to join dir and x to get the correct results.
In your third example, it does not work because os.path.abspath() also works with current directory, so if you do something like -
os.path.abspath('somefile')
The result produced would be - /path/to/current/directory/somefile - it does not validate if that is a real file/dir or not.
It is clearly stated in the documentation (Emphasis mine) -
os.path.abspath(path)
Return a normalized absolutized version of the pathname path. On most platforms, this is equivalent to calling the function normpath() as follows:
normpath(join(os.getcwd(), path)).
where os.getcwd() returns the path to current working directory.
回答2:
isfile() is looking in the current directory. Unless you include the directory name with the file name it has no idea where to find your files.
来源：https://stackoverflow.com/questions/32157127/os-path-isfile-doesnt-work-why