File Paths and Directory Operations

Understanding File Paths

A file path is like an address that tells Python where to find a file on your computer.

Two types of paths:

1. Absolute path - Full address from root

   • Windows: C:/Users/John/Documents/data.txt
   • Mac/Linux: /home/john/documents/data.txt

2. Relative path - Address from current location

   • data.txt (same folder as program)
   • files/data.txt (in files subfolder)
   • ../data.txt (in parent folder)

The os Module

Python's os module helps you work with files and folders.

import os

What this does: Imports the os module so you can use its functions.

Checking if File Exists

Before reading a file, check if it exists to avoid errors.

import os

if os.path.exists("data.txt"):
    print("File exists")
else:
    print("File not found")

What this does: Checks if data.txt exists before trying to open it.

Checking if Path is File or Folder

import os

path = "data.txt"

if os.path.isfile(path):
    print("This is a file")
elif os.path.isdir(path):
    print("This is a folder")
else:
    print("Path doesn't exist")

What these do:

• isfile() returns True if path is a file
• isdir() returns True if path is a directory (folder)

Getting Current Directory

Find out where your program is running from.

import os

current = os.getcwd()
print("Current directory:", current)

What getcwd() does: Gets Current Working Directory - the folder your program is running in.

Listing Files in Directory

See all files and folders in a directory.

import os

files = os.listdir()
print(files)

What this shows: List of all files and folders in current directory.

List files in specific folder:

files = os.listdir("documents")
print(files)

Filtering by File Type

import os

all_files = os.listdir()
txt_files = [f for f in all_files if f.endswith(".txt")]
print("Text files:", txt_files)

What this does: Shows only files that end with .txt extension.

Creating Directories

Make new folders using mkdir() or makedirs().

Create Single Directory

import os

os.mkdir("new_folder")
print("Folder created")

What this does: Creates a new folder named new_folder.

Note: If folder already exists, you get an error.

Create Nested Directories

import os

os.makedirs("data/reports/2024")
print("Folders created")

What this does: Creates data folder, then reports inside it, then 2024 inside reports. Creates all needed folders at once.

Safe Directory Creation

import os

folder = "my_data"
if not os.path.exists(folder):
    os.mkdir(folder)
    print("Folder created")
else:
    print("Folder already exists")

Why this is better: Checks first, so no error if folder exists.

Getting File Information

File Size

import os

size = os.path.getsize("data.txt")
print("File size:", size, "bytes")

What this shows: Size of the file in bytes.

Convert to KB or MB:

size_kb = size / 1024
size_mb = size / (1024 * 1024)
print("Size in KB:", size_kb)
print("Size in MB:", size_mb)

Last Modified Time

import os
import time

mod_time = os.path.getmtime("data.txt")
readable = time.ctime(mod_time)
print("Last modified:", readable)

What this shows: When the file was last changed.

Working with Paths

Joining Paths

Use os.path.join() to build paths correctly for any operating system.

import os

path = os.path.join("data", "reports", "file.txt")
print(path)

Why use join(): Windows uses backslash, Mac/Linux use forward slash. join() handles this automatically.

Getting File Name and Extension

import os

path = "data/reports/sales.txt"

filename = os.path.basename(path)
print("File name:", filename)

folder = os.path.dirname(path)
print("Folder:", folder)

name, ext = os.path.splitext(filename)
print("Name:", name)
print("Extension:", ext)

What these show:

• basename: sales.txt
• dirname: data/reports
• splitext: name=sales, ext=.txt

Getting Absolute Path

import os

relative = "data.txt"
absolute = os.path.abspath(relative)
print("Absolute path:", absolute)

What this does: Converts relative path to full absolute path.

Renaming and Deleting

Renaming Files

import os

os.rename("old_name.txt", "new_name.txt")
print("File renamed")

What this does: Changes file name from old_name.txt to new_name.txt.

Deleting Files

import os

if os.path.exists("temp.txt"):
    os.remove("temp.txt")
    print("File deleted")

What this does: Deletes temp.txt if it exists.

Warning: Be careful with remove() - deleted files cannot be recovered!

Deleting Empty Directories

import os

os.rmdir("empty_folder")
print("Folder deleted")

Note: rmdir() only works on empty folders.

The pathlib Module (Modern Approach)

Python 3.4+ has a newer, easier way to work with paths.

from pathlib import Path

path = Path("data.txt")

if path.exists():
    print("File exists")
    print("Size:", path.stat().st_size, "bytes")
    print("Is file:", path.is_file())

Why pathlib is nice: Uses object-oriented approach, cleaner syntax, easier to read.

Creating Paths with pathlib

from pathlib import Path

path = Path("data") / "reports" / "2024" / "sales.txt"
print(path)

What this does: Uses / operator to join path parts. Very readable!

Practice Example

The scenario: You're building a file organizer that sorts files by extension into folders.

import os

current_folder = os.getcwd()
print("Organizing files in:", current_folder)

files = os.listdir()
file_count = 0

for item in files:
    if os.path.isfile(item):
        file_count = file_count + 1
        name, ext = os.path.splitext(item)

        if ext:
            ext_folder = ext[1:]

            if not os.path.exists(ext_folder):
                os.mkdir(ext_folder)
                print("Created folder:", ext_folder)

            size = os.path.getsize(item)
            size_kb = size / 1024

            print("File:", item, "Size:", str(round(size_kb, 2)) + " KB")

print("Total files found:", file_count)

What this program does:

1. Gets current directory path
2. Lists all items in current folder
3. Checks each item if it's a file
4. Gets file extension
5. Creates folder for that extension if needed
6. Shows file name and size in KB
7. Counts total files processed

Note: This example shows how the code works but doesn't actually move files to avoid changing your system.

Key Points to Remember

Use os.path.exists() to check if file exists before accessing it. Use isfile() and isdir() to check if path is file or folder.

os.listdir() shows all files and folders in a directory. Filter results using list comprehension.

Use os.mkdir() for single folder, makedirs() for nested folders. Check existence first to avoid errors.

os.path.join() builds paths correctly for any operating system. Always use it instead of manually combining strings.

pathlib module (Path) is the modern, cleaner way to work with paths in Python 3.4 and newer.

Common Mistakes

Mistake 1: Wrong path separators

path = "data\\reports\\file.txt"  # Doesn't work on Mac/Linux
path = os.path.join("data", "reports", "file.txt")  # Works everywhere

Mistake 2: Forgetting to check existence

os.remove("file.txt")  # Error if file doesn't exist!

Fix:

if os.path.exists("file.txt"):
    os.remove("file.txt")

Mistake 3: Trying to delete non-empty folder

os.rmdir("folder")  # Error if folder has files!

Mistake 4: Not using absolute paths

with open("data.txt", "r") as file:  # Where is data.txt?

Better:

path = os.path.join(os.getcwd(), "data.txt")
with open(path, "r") as file:

What's Next?

You now know how to work with files, paths, and directories. Next, you'll learn about error handling with try-except - how to handle problems in your code gracefully without crashing.