Python 入门

Download and install the latest stable release from python.org. On macOS you can also use Homebrew, and on many Linux distributions Python is preinstalled.

python --version

You should see Python 3.11+ installed. If you see Python 2.x, use python3 instead of python.

pip installs packages from the Python Package Index. Confirm it is available:

pip --version

If not found, ensure Python 3 is installed or use the module form: python -m pip --version.

Create a file named hello.py with a single line:

echo 'print("Hello, Python!")' > hello.py

Run it:

python hello.py

You should see Hello, Python! printed to the terminal.

A virtual environment isolates your dependencies. Create one with the built‑in venv module:

python -m venv .venv

Activate it:

# macOS/Linux
source .venv/bin/activate

# Windows
.venv\Scripts\activate

With the venv active, packages you install stay local to the project.

Python’s basic types are simple and predictable:

# Numbers
42          # int
3.14        # float
1 + 2j      # complex

# Strings
"hello"      # double quotes
'hello'      # single quotes
"""multi
line"""     # triple quotes

# Booleans
True
False

Use + to concatenate strings and arithmetic operators for numbers.

Four essential containers cover most use cases:

# Lists: ordered, mutable
fruits = ["apple", "banana", "cherry"]
fruits.append("date")
fruits[0]  # "apple"

# Tuples: ordered, immutable
point = (3, 4)

# Sets: unordered, unique
tags = {"python", "tutorial"}
tags.add("basics")

# Dicts: key-value
user = {"name": "Ada", "score": 42}
user["name"]   # "Ada"

Pick a list when order matters, a dict when you have keys, and a set when uniqueness matters.

if/elif/else decides; for and while loop; break and continue steer execution:

score = 82
if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
else:
    grade = "C"

for i in range(3):
    print(i)

n = 5
while n > 0:
    n -= 1
    if n == 2:
        continue
    if n == 0:
        break

Use comprehensions for concise transformations over lists and dicts.

Encapsulate logic with def. Use type hints to document inputs and outputs:

def greet(name: str, excited: bool = False) -> str:
    msg = f"Hello, {name}!"
    return msg + "!" if excited else msg

print(greet("World"))
print(greet("Ada", True))

Default values let you call functions with fewer arguments, and return stops execution and yields a value.

Import code from other files or installed packages. Use from to keep namespaces tidy:

# math.py
PI = 3.14159
def area(r): return PI * r * r

# main.py
from math import area as circle_area
from mypackage import utils
print(circle_area(2))

A package is a directory with an __init__.py and modules inside.

You have the basics: install, run, types, control flow, functions, and modules. From here, explore:

• File I/O and the pathlib API
• Exceptions and graceful error handling
• Classes and object‑oriented design
• Testing with pytest
• Virtual environments and project layout (poetry, pipenv, or pip-tools)