Python 基本概念

1print("Hello World!")

 1# 1. Assigning values to variables
 2# Integer type variable
 3age = 25
 4print("Age:", age)  # Output: Age: 25
 5
 6# Floating-point type variable
 7height = 175.5
 8print("Height:", height, "cm")  # Output: Height: 175.5 cm
 9
10# String type variable
11name = "John"
12print("Name:", name)  # Output: Name: John
13
14# Boolean type variable
15is_student = True
16print("Are you a student?", is_student)  # Output: Are you a student? True
17
18# 2. Assigning values to multiple variables simultaneously
19# You can assign multiple variables at once
20x, y, z = 5, 10, 15
21print("x =", x, ", y =", y, ", z =", z)  # Output: x = 5 , y = 10 , z = 15
22
23# 3. Updating the value of a variable
24# The value of a variable can be updated by reassignment
25age = 26
26print("Updated age:", age)  # Output: Updated age: 26
27
28# 4. Updating multiple variables at once
29# Example of swapping values between variables
30a, b = 1, 2
31a, b = b, a
32print("a =", a, ", b =", b)  # Output: a = 2 , b = 1
33
34# 5. Type conversion
35# Type conversion allows operations between different types
36count = "5"  # String "5"
37count = int(count)  # Convert to integer type
38print("Handling count as an integer:", count * 2)  # Output: Handling count as an integer: 10
39
40# Conversion to floating-point number
41pi_approx = "3.14"
42pi_approx = float(pi_approx)
43print("Approximation of pi:", pi_approx)  # Output: Approximation of pi: 3.14

1# Example of integer type
2x = 10
3print(x)        # Output: 10
4print(type(x))  # Output: <class 'int'>

1# Floating Point Number Example
2y = 3.14
3print(y)        # Output: 3.14
4print(type(y))  # Output: float

1# Example of String
2s = "Hello, World!"
3print(s)        # Output: Hello, World!
4print(type(s))  # Output: <class 'str'>

1# Example of Boolean
2b = True
3print(b)        # Output: True
4print(type(b))  # Output: <class 'bool'>

1# Example of List
2lst = [1, 2, 3, "four", 5.0]
3print(lst)        # Output: [1, 2, 3, 'four', 5.0]
4print(type(lst))  # Output: <class 'list'>

1# Example of Tuple
2tup = (1, "two", 3.0)
3print(tup)        # Output: (1, 'two', 3.0)
4print(type(tup))  # Output: <class 'tuple'>

1# Example of Dictionary
2dct = {"one": 1, "two": 2, "three": 3}
3print(dct)        # Output: {'one': 1, 'two': 2, 'three': 3}
4print(type(dct))  # Output: <class 'dict'>

1# Example of Set
2st = {1, 2, 2, 3}
3print(st)        # Output: {1, 2, 3}
4print(type(st))  # Output: <class 'set'>

1# Example of escape characters
2print("Hello\nWorld")  # A newline is inserted after "Hello"
3
4# Output:
5# Hello
6# World

 1# String containing double quotes
 2quote = "He said, \"Python is amazing!\""
 3print(quote)
 4
 5# String containing single quotes
 6single_quote = 'It\'s a beautiful day!'
 7print(single_quote)
 8
 9# Output:
10# He said, "Python is amazing!"
11# It's a beautiful day!

 1# Example using newline
 2multiline_text = "First line\nSecond line"
 3print(multiline_text)
 4
 5# Example using tab
 6tabbed_text = "Column1\tColumn2\tColumn3"
 7print(tabbed_text)
 8
 9# Output:
10# First line
11# Second line
12# Column1	Column2	Column3

1# Example of Unicode escape
2japanese_text = "\u3053\u3093\u306B\u3061\u306F"  # Hello in Japanese
3print(japanese_text)
4# Output:
5# こんにちは(Hello in Japanese)

1raw_string = r"C:\Users\name\Documents"
2print(raw_string)
3# Output:
4# C:\Users\name\Documents

1# Example containing backslash
2path = "C:\\Program Files\\Python"
3print(path)
4# Output:
5# C:\Program Files\Python

 1# Example of formatting a message
 2message = "Dear User,\n\n\tThank you for your inquiry.\n\tWe will get back to you shortly.\n\nBest Regards,\nCustomer Support"
 3print(message)
 4# Output:
 5# Dear User,
 6#
 7#     Thank you for your inquiry.
 8#     We will get back to you shortly.
 9#
10#     Best Regards,
11#     Customer Support

1# Sample code that works in Python 1.0
2def greet(name):
3    print "Hello, " + name  # print was a statement
4
5greet("World")

1# Sample code that works in Python 2.0
2
3# List comprehension
4squares = [x * x for x in range(5)]
5print squares
6
7# Unicode string (u"...")
8greet = u"Hello"
9print greet

1# Sample code that works in Python 3.0
2
3# print is now a function
4print("Hello, world!")
5
6# Unicode text is handled natively
7message = "Hello"
8print(message)

1# Sample code that works in Python 3.5
2import asyncio
3
4async def say_hello():
5    await asyncio.sleep(1)
6    print("Hello, async world!")
7
8asyncio.run(say_hello())

1# Sample code that works in Python 3.6
2
3name = "Alice"
4age = 30
5print(f"{name} is {age} years old.")  # f-string makes formatting simple

 1# Sample code that works in Python 3.7
 2
 3from dataclasses import dataclass
 4
 5@dataclass
 6class Person:
 7    name: str
 8    age: int
 9
10p = Person("Bob", 25)
11print(p)

1# Sample code that works in Python 3.8
2
3# Assignment inside an expression
4if (n := len("hello")) > 3:
5    print(f"Length is {n}")

1# Sample code that works in Python 3.9
2
3a = {"x": 1}
4b = {"y": 2}
5c = a | b  # merge two dicts
6print(c)   # {'x': 1, 'y': 2}

 1# Sample code that works in Python 3.10
 2
 3def handle(value):
 4    match value:
 5        case 1:
 6            return "One"
 7        case 2:
 8            return "Two"
 9        case _:
10            return "Other"
11
12print(handle(2))

1# Sample code that works in Python 3.11
2
3# Improved performance (up to 25% faster in general)
4# More informative error messages
5try:
6    eval("1/0")
7except ZeroDivisionError as e:
8    print(f"Caught an error: {e}")

 1# Sample code that works in Python 3.12
 2
 3# Automatically shows exception chains with detailed traceback
 4def f():
 5    raise ValueError("Something went wrong")
 6
 7def g():
 8    try:
 9        f()
10    except Exception:
11        raise RuntimeError("Higher level error")  # Automatically chained
12
13try:
14    g()
15except Exception as e:
16    import traceback
17    traceback.print_exception(type(e), e, e.__traceback__)

 1# Sample code that works in Python 3.13
 2
 3# Using the new 'except*' syntax for handling multiple exceptions in parallel
 4import asyncio
 5
 6async def raise_errors():
 7    raise ExceptionGroup("Multiple errors", [
 8        ValueError("Invalid value"),
 9        TypeError("Wrong type"),
10    ])
11
12async def main():
13    try:
14        await raise_errors()
15    except* ValueError as e:
16        print("Caught ValueError(s):", e.exceptions)
17    except* TypeError as e:
18        print("Caught TypeError(s):", e.exceptions)
19
20asyncio.run(main())