Python | os.path.commonpath() method

OS module in Python provides functions for interacting with the operating system. OS comes under Python’s standard utility modules. This module provides a portable way of using operating system dependent functionality. os.path module is submodule of OS module in Python used for common path name manipulation.

os.path.commonpath() method in Python is used to get the longest common sub-path in a list of paths. This method raise ValueError if the specified list of paths either contains both absolute and relative path, or is empty. Unlike os.path.commonpath() method, the returned value is a valid path.
For example consider the following list of paths:

          list of paths                     Longest common sub-path
['/home/User/Photos', /home/User/Videos']        /home/User          
['/usr/local/bin', '/usr/lib']                   /usr               

Syntax: os.path.commonpath(list)

Parameter:
path: A list of path-like object. A path-like object is either a string or bytes object representing a path.

Return Type: This method returns a string value which represents the longest common sub-path in the specified list.

Code #1: Use of os.path.commonpath() method

# Python program to explain os.path.commonpath() method

# importing os module
import os

# List of Paths
paths = ['/home/User/Desktop', '/home/User/Documents',
         '/home/User/Downloads']

# Get the
# longest common sub-path
# in the specified list
prefix = os.path.commonpath(paths)


# Print the
# longest common sub-path
# in the specified list
print("Longest common sub-path:", prefix)


# List of Paths
paths = ['/usr/local/bin', '/usr/bin']

# Get the
# longest common sub-path
# in the specified list
prefix = os.path.commonpath(paths)


# Print the
# longest common sub-path
# in the specified list
print("Longest common sub-path:", prefix)

Output:

Longest common sub-path: /home/User
Longest common sub-path: /usr

Code #2: Use of os.path.commonpath() method

# Python program to explain os.path.commonpath() method

# importing os module
import os

# List of Paths
paths = ['/usr/local/bin', 'usr/bin']

# Get the
# longest common sub-path
# in the specified list
prefix = os.path.commonpath(paths)


# Print the
# longest common sub-path
# in the specified list
print("Longest common sub-path:", prefix)


# The above code will raise
# ValueError as list of paths
# contains both absolute and
# relative path

Output:

Traceback (most recent call last):
  File "oscommonpath.py", line 12, in 
    prefix = os.path.commonpath(paths)
  File "/usr/lib/python3.6/posixpath.py", line 505, in commonpath
    raise ValueError("Can't mix absolute and relative paths") from None
ValueError: Can't mix absolute and relative paths

Note: If the specified list is empty, os.path.commonpath() method will raise ValueError too.

Reference: https://docs.python.org/3/library/os.path.html