Files and folders · Computer Basics
Where does a photo go when you save it, and how do you find it again?
Course contentsWhy you need it
Storage holds millions of things. Files and folders are how you, and every program, keep them in order and find them again.
Later your programs will open files by their path, and the Linux course is all about moving between folders. Knowing the idea now makes all of that easy.
The intuition
A file is one saved thing with a name: a photo, a song, a document, a program. A folder (also called a directory) is a container that holds files and other folders. Folders inside folders make a tree:
/ the top
└── Users
└── mia
├── Documents
│ └── cv.docx
└── Pictures
├── beach.jpg
└── 2024
└── cat.pngTo say exactly where a file is, write its path: the folders from the top down to it, separated by /:
/Users/mia/Pictures/2024/cat.png
It's like a postal address read from the country down to the house number. On Windows a path starts with a drive letter and uses backslashes, like C:\Users\mia\Pictures\cat.png, but it's the same idea.
File extensions. The part after the last dot says what kind of file it is: .jpg and .png are pictures, .mp3 is sound, .mp4 is video, .pdf and .docx are documents, .txt is plain text and .py is a Python program. Inside, every file is just bytes; the extension tells programs how to read them.
Definition
File
A file is a named collection of data kept in storage, such as a photo, a document or a program.
Folder (directory)
A folder, or directory, is a container that holds files and other folders.
Path
A path is the address of a file or folder: the folders from the top down to it, separated by slashes.
Examples
Build a path
Try it yourselfPut the folders in order from the top, then the file name. Add a folder to the list (in quotes, with a comma) and see the path grow.
folders = ["Users", "mia", "Pictures"] # change me 改这里
file = "cat.png"
path = ""
for name in folders:
path = path + "/" + name
path = path + "/" + file
print(path)- L1The folders, from the top down.
["Users", "mia", "Pictures"] - L5Add each folder with a / in front.
path = /Users - L5Keep going down the tree.
path = /Users/mia/Pictures - L6The file name goes last.
path = /Users/mia/Pictures/cat.png
Draw a path as a tree
Try it yourselfThe opposite job: cut a path at every / and draw each part one level deeper. Paste in a path of your own.
path = "/Users/mia/Documents/school/report.docx" # change me 改这里
parts = path.split("/")[1:]
depth = 0
for part in parts[:-1]:
print(" " * depth + part + "/")
depth = depth + 1
print(" " * depth + parts[-1])- L2Cut the path at every /.
Users | mia | Documents | school | report.docx - L5Every folder is drawn one level deeper than the one before.
Users/ - L7The file sits inside the last folder.
report.docx
What kind of file?
Try it yourselfThe machine looks only at the extension, the part after the last dot. Try song.mp3, notes.txt or game.exe.
name = "holiday.mp4" # change me 改这里
kinds = {"jpg": "a picture", "png": "a picture", "mp3": "sound",
"mp4": "a video", "txt": "plain text", "pdf": "a document",
"py": "a Python program"}
extension = name.split(".")[-1]
print(name, "is", kinds.get(extension, "a kind of file this machine doesn't know"))- L1The file name.
name = "holiday.mp4" - L5Take the part after the last dot.
extension = "mp4" - L6Look it up in the table.
holiday.mp4 is a video
Common mistakes
Renaming the extension doesn't convert the file
Renaming song.mp3 to song.mp4 doesn't turn music into a video; the bytes inside stay the same. It only confuses programs about how to open it.
Same name, different folders
/Users/mia/notes.txt and /Users/sam/notes.txt are two different files: the path, not just the name, says which file you mean. Inside one folder, though, every name must be different.
Hidden extensions
Many computers hide extensions, so photo.jpg shows up as just photo. Turn on "show file name extensions" in your file manager's settings to see them.
Quick quiz
1. In /Users/mia/Music/song.mp3, which folder is song.mp3 directly inside?
Show the answer
Answer: C
The folder just before the file name holds it: Music. mia holds Music, and Users holds mia.
2. Which file is most likely a picture?
Show the answer
Answer: B
.jpg is a picture format. .txt is plain text and .mp3 is sound.
3. Can two files both be called notes.txt?
Show the answer
Answer: B
Different folders give them different paths, so the computer can tell them apart. In the same folder they would clash.
Key points
- A file is saved data with a name; folders hold files and other folders, forming a tree.
- A path like
/Users/mia/Pictures/cat.pngsays exactly where a file is. - The extension (
.jpg,.mp3,.pdf…) says what kind of file it is.
Practice
3 short exercises: think it through, change something and see what happens, then do one yourself. Answers are checked the moment you submit.
- ThinkFind the path
Here is part of a computer's folder tree:
/ └── home └── leo ├── games │ └── chess.py └── music └── rain.mp3What is the path of
rain.mp3? - ChangeThe photo moved
Mia made a new folder called
petsinsidePicturesand movedcat.pnginto it.Change the folder list so the machine prints the new path:
/Users/mia/Pictures/pets/cat.png - Your turnWrite the path
Here is Ana's computer:
/ └── Users └── ana ├── Desktop └── Documents └── 2025 └── taxes.pdfWrite the full path of
taxes.pdf.
Practise this lesson
Open the interactive lesson to edit and run these examples and solve the exercises with instant feedback. Free to start, no sign-up.
Interactive lessons open in order. If you have not done the earlier ones yet, you start at the course map.
Terms in this lesson
| Term | Chinese | Definition |
|---|---|---|
| File | 文件 | A named piece of data kept in storage. |
| Folder (directory) | 文件夹（目录） | A container that holds files and other folders. |
| Path | 路径 | The address of a file: the folders from the top down to it, separated by slashes. |
| File extension | 扩展名 | The end of a file name after the last dot, such as .jpg, which says what kind of file it is. |