Python 基本语法和缩进：完整的初学者指南

# this is a comment - python ignores anything after the '#' symbolstudent_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.")

# basic math operationstotal_score = 95 + 87    # additionaverage = total_score / 2 # division# comparisonsif student_age >= 15:    print(f"{student_name} can take advanced classes")

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

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

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")

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")

# good: clear and easy to followdef 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 levelsdef 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"

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")

# wrong - inconsistent indentationif score > 90:print("great job!")    # error: no indentation    print("keep it up!")   # error: inconsistent indentation# right - proper indentationif score > 90:    print("great job!")    print("keep it up!")

# 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

def grade_assignment(score, late_days):    # Start with the base score    final_score = score    # Check if the assignment is late    if late_days > 0:        if late_days <= 5:            # Deduct 2 points per late day            final_score -= (late_days * 2)        else:            # Maximum lateness penalty            final_score -= 10    # Ensure score doesn't go below 0    if final_score < 0:        final_score = 0    # Determine letter grade    if final_score >= 90:        return "A", final_score    elif final_score >= 80:        return "B", final_score    elif final_score >= 70:        return "C", final_score    else:        return "F", final_score# Test the functionscore = 95late_days = 2letter_grade, final_score = grade_assignment(score, late_days)print(f"Original Score: {score}")print(f"Late Days: {late_days}")print(f"Final Score: {final_score}")print(f"Letter Grade: {letter_grade}")