字符串字面量

python 中的字符串字面量由单引号或双引号括起。

'hello' 等同于 "hello"。

您可以使用 print() 函数显示字符串字面量：

示例代码：

print("Hello")
print('Hello')

完整实例：

#You can use double or single quotes:
print("Hello")
print('Hello')

用字符串向变量赋值

通过使用变量名称后跟等号和字符串，可以把字符串赋值给变量：

示例代码：

a = "Hello"
print(a)

完整实例：

a = "Hello"
print(a)

多行字符串

您可以使用三个引号将多行字符串赋值给变量：

示例代码：

您可以使用三个双引号：

a = """Python is a widely used general-purpose, high level programming language.
It was initially designed by Guido van Rossum in 1991
and developed by Python Software Foundation.
It was mainly developed for emphasis on code readability,
and its syntax allows programmers to express concepts in fewer lines of code."""
print(a)

完整实例：

a = """Python is a widely used general-purpose, high level programming language.
It was initially designed by Guido van Rossum in 1991
and developed by Python Software Foundation.
It was mainly developed for emphasis on code readability,
and its syntax allows programmers to express concepts in fewer lines of code."""
print(a)

或三个单引号：

示例代码：

a = '''Python is a widely used general-purpose, high level programming language.
It was initially designed by Guido van Rossum in 1991
and developed by Python Software Foundation.
It was mainly developed for emphasis on code readability,
and its syntax allows programmers to express concepts in fewer lines of code.'''
print(a)

完整实例：

a = '''Python is a widely used general-purpose, high level programming language.
It was initially designed by Guido van Rossum in 1991
and developed by Python Software Foundation.
It was mainly developed for emphasis on code readability,
and its syntax allows programmers to express concepts in fewer lines of code.'''
print(a)

注释：在结果中，换行符插入与代码中相同的位置。

字符串是数组

像许多其他流行的编程语言一样，Python 中的字符串是表示 unicode 字符的字节数组。

但是，Python 没有字符数据类型，单个字符就是长度为 1 的字符串。

方括号可用于访问字符串的元素。

示例代码：

获取位置 1 处的字符（请记住第一个字符的位置为 0）：

a = "Hello, World!"
print(a[1])

完整实例：

a = "Hello, World!"
print(a[1])

裁切

您可以使用裁切语法返回一定范围的字符。

指定开始索引和结束索引，以冒号分隔，以返回字符串的一部分。

示例代码：

获取从位置 2 到位置 5（不包括）的字符：

b = "Hello, World!"
print(b[2:5])

完整实例：

b = "Hello, World!"
print(b[2:5])

负的索引

使用负索引从字符串末尾开始切片：

示例代码：

获取从位置 5 到位置 1 的字符，从字符串末尾开始计数：

b = "Hello, World!"
print(b[-5:-2])

完整实例：

b = "Hello, World!"
print(b[-5:-2])

字符串长度

如需获取字符串的长度，请使用 len() 函数。

示例代码：

len() 函数返回字符串的长度：

a = "Hello, World!"
print(len(a))

完整实例：

a = "Hello, World!"
print(len(a))

字符串方法

Python 有一组可用于字符串的内置方法。

示例代码：

strip() 方法删除开头和结尾的空白字符：

a = " Hello, World! "
print(a.strip()) # returns "Hello, World!"

完整实例：

a = " Hello, World! "
print(a.strip())

示例代码：

lower() 返回小写的字符串：

a = "Hello, World!"
print(a.lower())

完整实例：

a = "Hello, World!"
print(a.lower())

示例代码：

upper() 方法返回大写的字符串：

a = "Hello, World!"
print(a.upper())

完整实例：

a = "Hello, World!"
print(a.upper())

示例代码：

replace() 用另一段字符串来替换字符串：

a = "Hello, World!"
print(a.replace("World", "Kitty"))

完整实例：

a = "Hello, World!"
print(a.replace("World", "Kitty"))

示例代码：

split() 方法在找到分隔符的实例时将字符串拆分为子字符串：

a = "Hello, World!"
print(a.split(",")) # returns ['Hello', ' World!']

完整实例：

a = "Hello, World!"
b = a.split(",")
print(b)

请使用我们的字符串方法参考手册，学习更多的字符串方法。

检查字符串

如需检查字符串中是否存在特定短语或字符，我们可以使用 in 或 not in 关键字。

示例代码：

检查以下文本中是否存在短语 "ina"：

txt = "China is a great country"
x = "ina" in txt
print(x)

完整实例：

txt = "China is a great country"
x = "ina" in txt
print(x)

示例代码：

检查以下文本中是否没有短语 "ina"：

txt = "China is a great country"
x = "ain" not in txt
print(x) 

完整实例：

txt = "China is a great country"
x = "ain" not in txt
print(x)

字符串级联（串联）

如需串联或组合两个字符串，您可以使用 + 运算符。

示例代码：

将变量 a 与变量 b 合并到变量 c 中：

a = "Hello"
b = "World"
c = a + b
print(c)

完整实例：

a = "Hello"
b = "World"
c = a + b
print(c)

示例代码：

在它们之间添加一个空格：

a = "Hello"
b = "World"
c = a + " " + b
print(c)

完整实例：

a = "Hello"
b = "World"
c = a + " " + b
print(c)

字符串格式

正如在 Python 变量一章中所学到的，我们不能像这样组合字符串和数字：

示例代码：

age = 63
txt = "My name is Bill, I am " + age
print(txt)

完整实例：

age = 36
txt = "My name is Bill, I am " + age
print(txt)

但是我们可以使用 format() 方法组合字符串和数字！

format() 方法接受传递的参数，格式化它们，并将它们放在占位符 {} 所在的字符串中：

示例代码：

使用 format() 方法将数字插入字符串：

age = 63
txt = "My name is Bill, and I am {}"
print(txt.format(age))

完整实例：

age = 63
txt = "My name is Bill, and I am {}"
print(txt.format(age))

format() 方法接受不限数量的参数，并放在各自的占位符中：

示例代码：

quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))

完整实例：

quantity = 5
itemno = 789
price = 24.36
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))

您可以使用索引号 {0} 来确保参数被放在正确的占位符中：

示例代码：

quantity = 3
itemno = 567
price = 49.95
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))

完整实例：

quantity = 5
itemno = 789
price = 24.36
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))

字符串方法

Python 有一组可以在字符串上使用的内建方法。

注释：所有字符串方法都返回新值。它们不会更改原始字符串。

注释：所有字符串方法都返回新值。它们不会更改原始字符串。