Unit 20: Folders & Paths
Finding your way around.
Unit 20 of 31 in Python for kids. Its 4 lessons are Paths as Objects, Making Folders, Looking Inside and Folder Master — below is everything each one explains, and a question or two from it to try.
Every sample on this page was run through real Python before it shipped, and prints exactly what it says it prints.
This unit opens with a fortnight’s trial of everything — no card needed — or with a family plan, bought in the iPhone app. The first two units of every track are free for ever. Try it in the app.
🧭 Paths as Objects
A path that knows things about itself
A filename is just text, and text cannot answer questions. A Path from the pathlib module can — whether it exists, what it is called, what kind of file it is.
Python
from pathlib import Path
p = Path("story.txt")
print(p.name)
print(p.suffix)
print(p.exists())It prints
story.txt .txt False
Reading and writing in one line
write_text and read_text do the whole job — opening, writing and closing — without a with block.
Python
from pathlib import Path
p = Path("hello.txt")
p.write_text("Hi there\n")
print(p.read_text().strip())
print(p.exists())It prints
Hi there True
Joining with a slash
A / between paths joins them — and it gets the separator right on every kind of computer, which glueing text together does not.
Python
from pathlib import Path
folder = Path("photos")
picture = folder / "cat.png"
print(picture)
print(picture.name)It prints
photos/cat.png cat.png
Try it yourself
Why use Path instead of a plain string filename?
- It is shorter to type
- A Path can answer questions about itself and join safely onto other paths
- Strings do not work for filenames
- It is required in Python 3
What does this print?
Python
from pathlib import Path
p = Path("notes") / "day1.md"
print(p.suffix)
print(p.stem)Answer them in the app
📁 Making Folders
A folder to keep things in
mkdir makes a folder. exist_ok=True means "do not complain if it is already there", which saves checking first.
Python
from pathlib import Path
folder = Path("homework")
folder.mkdir(exist_ok=True)
print(folder.exists())
print(folder.is_dir())It prints
True True
Putting files inside
Join the folder to a filename with /, and write as usual.
Python
from pathlib import Path
folder = Path("homework")
folder.mkdir(exist_ok=True)
(folder / "maths.txt").write_text("sums\n")
print((folder / "maths.txt").read_text().strip())It prints
sums
Folders inside folders
parents=True makes every folder along the way, so you can build a whole path at once.
Python
from pathlib import Path
p = Path("school/year6/art")
p.mkdir(parents=True, exist_ok=True)
print(p.exists())It prints
True
Try it yourself
What does exist_ok=True do?
- Deletes the folder first
- Stops it complaining when the folder is already there
- Makes the folder hidden
- Checks the folder is empty
Answer it in the app
🔦 Looking Inside
What is in there?
iterdir walks through everything in a folder. Sort the names, because the order the computer hands them back in is not guaranteed.
Python
from pathlib import Path
folder = Path("box")
folder.mkdir(exist_ok=True)
(folder / "b.txt").write_text("2")
(folder / "a.txt").write_text("1")
print(sorted(f.name for f in folder.iterdir()))It prints
['a.txt', 'b.txt']
Only the ones you want
glob matches a pattern. * means "anything", so *.txt finds every text file and ignores the rest.
Python
from pathlib import Path
folder = Path("box")
folder.mkdir(exist_ok=True)
(folder / "note.txt").write_text("a")
(folder / "photo.png").write_text("b")
print(sorted(f.name for f in folder.glob("*.txt")))It prints
['note.txt']
The older way you will still see
os.listdir does much the same thing and turns up in a lot of code. It gives plain text names rather than paths, so you have to join them back on yourself.
Python
import os
from pathlib import Path
Path("box").mkdir(exist_ok=True)
(Path("box") / "a.txt").write_text("1")
print(sorted(os.listdir("box")))It prints
['a.txt']
Try it yourself
What does the * in "*.txt" mean?
- Multiply
- Any name at all, as long as it ends in .txt
- Exactly one letter
- All folders
Answer it in the app
🏆 Folder Master
Try it yourself
What does this print?
Python
from pathlib import Path
p = Path("music") / "song.mp3"
print(p.stem)
print(p.suffix)
print(p.parent)Answer it in the app