Simplify a File Path in Python with a Stack

Uses a stack to normalize an absolute Unix path by handling '.', '..', and duplicate slashes.

Easy Python 3.8+ Aug 9, 2026 Algorithms & data structures 11 views 0 copies

stack string path algorithm

Python code

28 lines

Python 3.8+

from pathlib import PurePosixPath

def simplify_path(path: str) -> str:
    tokens = path.split('/')
    stack = []
    
    for token in tokens:
        if not token or token == '.':
            continue
        if token == '..':
            if stack:
                stack.pop()
        else:
            stack.append(token)
    
    return '/' + '/'.join(stack)


if __name__ == "__main__":
    paths = [
        "/home/",
        "/a/./b/../../c/",
        "/../",
        "/home//foo/",
        "/a/b/c/../../../"
    ]
    for p in paths:
        print(f"simplify_path('{p}') = '{simplify_path(p)}'")

Output

stdout

simplify_path('/home/') = '/home'
simplify_path('/a/./b/../../c/') = '/c'
simplify_path('/../') = '/'
simplify_path('/home//foo/') = '/home/foo'
simplify_path('/a/b/c/../../../') = '/'

How it works

The path is split on '/' so each component becomes a token. Empty tokens (from duplicate slashes) and '.' are ignored because they don't change the directory. When a '..' appears, we pop the last directory from the stack to go up one level, but only if the stack isn't empty to avoid going above root. After processing, the stack contains the valid directory components, and joining them with '/' and prepending '/' reconstructs the simplified path.

Common mistakes

Popping from an empty stack when '..' appears at root
Forgetting to handle empty tokens from duplicate slashes
Hardcoding os.path functions instead of implementing the algorithm
Not considering that '.' and '..' can appear mid-string

Variations

Use os.path.normpath for a built-in solution
Use a list as the stack and join at the end instead of a deque

Real-world use cases

Normalizing URLs in a web scraper or crawler before storing or fetching links.
Cleaning user input file paths in a CLI tool before accessing filesystem resources.
Resolving relative paths in a build system to determine absolute targets.

Simplify a File Path in Python with a Stack

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Algorithms & data structures

Tutorials

Quizzes

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Algorithms & data structures

Keep learning

Tutorials

Quizzes