Introduction

Let's look at a simple use-case. The following function uses the PyFilesystem API to count the number of non-blank lines of Python code in a directory (and any subdirectories):

def count_python_loc(fs):
    """Count non-blank lines of Python code."""
    count = 0
    for path in fs.walk.files(filter=['*.py']):
        with fs.open(path) as python_file:
            count += sum(1 for line in python_file if line.strip())
    return count

The above code can be made to work with any filesystem, here are just a few examples:

# HD
with open_fs('.') as fs:
    print(count_python_loc(fs))

# Zip file
with open_fs('zip://projects.zip') as fs:
    print(count_python_loc(fs))

# FTP Server
with open_fs('ftp://ftp.example.org/projects') as fs:
    print(count_python_loc(fs))

Contrast that with the equivalent code using just the standard library:

def count_python_loc(path):
    """Count non-blank lines of Python code."""
    count = 0
    for root, dirs, files in os.walk(path):
        for name in files:
            if name.endswith('.py'):
                with open(os.path.join(root, name), 'rt') as python_file:
                    count += sum(1 for line in python_file if line.strip())
    return count

This version will only work with the local drive. Any other filesystem would require a different API and likely re-implementing the functionality of os.walk.