Python 基本語法與縮排：完整的初學者指南-Python教學-PHP中文網

Python Basic Syntax and Indentation: The Complete Beginner

當你第一次學習程式設計時，Python 因一個特殊原因而脫穎而出：它的設計理念是幾乎像英語一樣閱讀。與使用大量符號和括號的其他程式語言不同，Python 依賴簡單、乾淨的格式，使您的程式碼看起來像一個組織良好的文件。

將 Python 的語法視為語言的語法規則。正如英語有關於如何構造句子以使含義清晰的規則一樣，Python 也有關於如何編寫程式碼以便人類和電腦都能理解的規則。

理解Python的基本語法

建構模組

讓我們從最簡單的 Python 語法元素開始：

# This is a comment - Python ignores anything after the '#' symbol
student_name = "Alice"    # A variable holding text (string)
student_age = 15         # A variable holding a number (integer)

# Using variables in a sentence (string formatting)
print(f"Hello, my name is {student_name} and I'm {student_age} years old.")

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在這個範例中，我們使用了 Python 的幾個基本元素：

註解（以#開頭的行）
變數（student_name 和 Student_age）
字串格式（f"..." 語法）
列印功能

基本操作

Python可以像計算器一樣計算與比較：

# Basic math operations
total_score = 95 + 87    # Addition
average = total_score / 2 # Division

# Comparisons
if student_age >= 15:
    print(f"{student_name} can take advanced classes")

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Python 的核心：理解縮排

這就是 Python 真正獨特的地方：Python 使用縮排，而不是使用括號或特殊符號將程式碼組合在一起。乍看之下這可能看起來很奇怪，但它使 Python 程式碼異常清晰易讀。

縮排如何建立結構

將縮排想為組織詳細大綱的方式：

def make_sandwich():
    print("1. Get two slices of bread")  # First level
    if has_cheese:
        print("2. Add cheese")           # Second level
        print("3. Add tomatoes")         # Still second level
    else:
        print("2. Add butter")           # Second level in else block
    print("4. Put the slices together")  # Back to first level

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每個縮排區塊都告訴 Python「這些行屬於一起」。這就像在大綱中創建一個子列表 - “if has_cheese:”下縮排的所有內容都是該條件的一部分。

縮排規則

我們來看看Python縮排的關鍵規則：

def process_grade(score):
    # Rule 1: Use exactly 4 spaces for each indentation level
    if score >= 90:
        print("Excellent!")
        if score == 100:
            print("Perfect score!")

    # Rule 2: Aligned blocks work together
    elif score >= 80:
        print("Good job!")
        print("Keep it up!")  # This line is part of the elif block

    # Rule 3: Unindented lines end the block
    print("Processing complete")  # This runs regardless of score

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嵌套縮排：更深入

隨著您的程式變得更加複雜，您通常需要多層縮排：

def check_weather(temperature, is_raining):
    # First level: inside function
    if temperature > 70:
        # Second level: inside if
        if is_raining:
            # Third level: nested condition
            print("It's warm but raining")
            print("Take an umbrella")
        else:
            print("It's a warm, sunny day")
            print("Perfect for outdoors")
    else:
        print("It's cool outside")
        print("Take a jacket")

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複雜的結構和壓痕

讓我們來看一個更複雜的範例，它展示了縮排如何幫助組織程式碼：

def process_student_grades(students):
    for student in students:            # First level loop
        print(f"Checking {student['name']}'s grades...")

        total = 0
        for grade in student['grades']: # Second level loop
            if grade > 90:              # Third level condition
                print("Outstanding!")
            total += grade

        average = total / len(student['grades'])

        # Back to first loop level
        if average >= 90:
            print("Honor Roll")
            if student['attendance'] > 95:  # Another level
                print("Perfect Attendance Award")

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常見模式和最佳實踐

處理多種條件

# Good: Clear and easy to follow
def check_eligibility(age, grade, attendance):
    if age < 18:
        return "Too young"

    if grade < 70:
        return "Grades too low"

    if attendance < 80:
        return "Attendance too low"

    return "Eligible"

# Avoid: Too many nested levels
def check_eligibility_nested(age, grade, attendance):
    if age >= 18:
        if grade >= 70:
            if attendance >= 80:
                return "Eligible"
            else:
                return "Attendance too low"
        else:
            return "Grades too low"
    else:
        return "Too young"

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使用函數和類別

class Student:
    def __init__(self, name):
        self.name = name
        self.grades = []

    def add_grade(self, grade):
        # Notice the consistent indentation in methods
        if isinstance(grade, (int, float)):
            if 0 <= grade <= 100:
                self.grades.append(grade)
                print(f"Grade {grade} added")
            else:
                print("Grade must be between 0 and 100")
        else:
            print("Grade must be a number")

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常見錯誤及其解決方法

縮排錯誤

# WRONG - Inconsistent indentation
if score > 90:
print("Great job!")    # Error: no indentation
    print("Keep it up!")   # Error: inconsistent indentation

# RIGHT - Proper indentation
if score > 90:
    print("Great job!")
    print("Keep it up!")

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混合製表符和空格

# WRONG - Mixed tabs and spaces (don't do this!)
def calculate_average(numbers):
    total = 0
    count = 0    # This line uses a tab
    for num in numbers:    # This line uses spaces
        total += num

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練習：將它們放在一起

嘗試寫這個程式來練習縮排和文法：

# This is a comment - Python ignores anything after the '#' symbol
student_name = "Alice"    # A variable holding text (string)
student_age = 15         # A variable holding a number (integer)

# Using variables in a sentence (string formatting)
print(f"Hello, my name is {student_name} and I'm {student_age} years old.")

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