Paths and Folders with pathlib

Why this matters

Programs need to find files and folders, build paths, check what exists, and list what is in a directory. Joining paths with plain strings ("data" + "/" + "x.txt") breaks on Windows. The pathlib module gives paths that work everywhere and read nicely.

The idea

from pathlib import Path

folder = Path("notes")
file = folder / "todo.txt"        # the / operator joins path pieces
print(file)                       # notes/todo.txt  (notes\todo.txt on Windows)

file.name       # 'todo.txt'
file.stem       # 'todo'
file.suffix     # '.txt'
file.parent     # Path('notes')

folder.mkdir(exist_ok=True)       # create the folder (no error if it exists)
file.write_text("buy milk\n")     # write a whole file in one line
print(file.read_text())           # read a whole file in one line
print(file.exists())              # True

for item in folder.glob("*.txt"): # every match for a pattern
    print(item.name)

Path.iterdir() lists everything in a folder, and glob("*.txt") lists only the matches. Neither guarantees an order, so use sorted(...) when order matters. A Path works anywhere open() expects a filename.

Try it

Make a folder, put three .txt files and one .csv file in it with write_text, and print the names of just the text files, sorted.

Your turn

Write three functions. Each is given a folder or path (the checks use temporary ones):

• notes_path(folder, name): the path of the file called name plus .txt inside folder. Return a Path.
• list_text_files(folder): the names of the .txt files in the folder, sorted, as a list of strings.
• copy_text(source, destination): copy the text from one file into another. The destination’s folder may not exist yet: create it.

Recap

• Path("a") / "b.txt" builds paths safely; .name, .stem, .suffix, .parent take them apart.
• .exists(), .mkdir(), .read_text(), .write_text() and .glob() cover most jobs.
• Sort listings when order matters.

Common mistakes

• Building paths by hand with "/" or "\\" in strings.
• Assuming listing order. It differs between computers.
• mkdir on an existing folder raises FileExistsError unless you pass exist_ok=True.