一、案例1：最基础的字符串替换

text = "Hello World"
new_text = text.replace("World", "Python")
print(text)       # 输出: Hello World
print(new_text)   # 输出: Hello Python

二、案例2：控制替换次数

text = "apple apple apple"
new_text = text.replace("apple", "banana", 2)
print(new_text)  
# 输出：banana banana apple

三、案例3：多层替换

text = "the sky is blue, the sea is also blue"
new_text = text.replace("blue", "green").replace("sea", "ocean")
print(new_text)  
# 输出：the sky is green, the ocean is also green