At this point you know everything you need to handle text files in Python. However, there are several handy functions that make your life easier when dealing with files. These are collected in the os.path module. As per usual, I am not going to list all of them, but I will list the ones that you will use the most.

In these functions, the term “path” refers to a filename or a directory name, complete with parent directories (and drive letter). The parent directories (and drive letter) do not need to be there explicitly, but even if they are not, implicitly they still are as each file and each directory is located in a particular place in the file system.

exists()

The function exists() gets a path as argument, and returns True if that path exists, and False if it does not.

from os.path import exists

if exists( "pc_rose.txt" ):
    print( "Rose exists" )
else:
    print( "Rose does not exist" )

if exists( "pc_tulip.txt" ):
    print( "Tulip exists" )
else:
    print( "Tulip does not exist" )

isfile()

isfile() tests if the path that is supplied as argument is a file. If it is, it returns True. If it is not, it returns False. If the path does not exist, the function also returns False.

from os.path import isfile

if isfile( "pc_rose.txt" ):
    print( "Rose is a file" )
else:
    print( "Rose is not a file" )

isdir()

isdir() tests if the path that is supplied as argument is a directory. If it is, it returns True. If it is not, it returns False. If the path does not exist, the function also returns False.

from os.path import isdir

if isdir( "pc_rose.txt" ):
    print( "Rose is a directory" )
else:
    print( "Rose is not a directory" )

join()

join() takes one or more parts of a path as argument, and concatenates them reasonably intelligently to a legal name for a path, which it returns. This means that it will add and remove slashes as needed. join() is particularly handy in combination with listdir() (see Chapter 16¹, and the example below).

The reason that join() is handy with listdir(), is that listdir() results in a list of file names that do not include the directory names. Usually, when you ask for a list of file names, you intend to open them at some point. But to open a file that is not in the current directory, you need to know the complete path name that leads to the file. When you apply listdir(), you know where you are looking for files, so you know the elements of the path name. To construct the complete path name for each file, you need to concatenate the elements of the path name to the file name. Rather than trying to decide where you need to add slashes, and which kind of slashes they need to be, you can leave all of that to the join() function.

The code below looks for all the files in the current directory, and lists them including their complete path name. See how join() is used to construct that path name from the current directory, and the file name.

from os import listdir, getcwd
from os.path import join

filelist = listdir( "." )
for name in filelist:
    pathname = join( getcwd(), name )
    print( pathname )

basename()

basename() extracts the filename from a path, and returns it.

from os.path import basename

print( basename( "/System/Home/readme.txt" ) )

dirname()

dirname() extracts the directory name from a path, and returns it.

from os.path import dirname

print( dirname( "/System/Home/readme.txt" ) )

getsize()

getsize() gets the size of the file that is supplied as argument, and returns it as an integer (representing a number of bytes). The file must exist, otherwise you get a runtime error.

from os.path import getsize

numbytes = getsize( "pc_rose.txt" )
print( numbytes )

Write a program that adds up the sizes of all the files in the current directory, and prints the result.