• Python3 格式化字符串


    Python3 格式化字符串

    在Python 3.6之前,有两种将Python表达式嵌入到字符串文本中进行格式化的主要方法:%-formattingstr.format()

    一、%-formatting

    name = "Eric"
    age = 74
    "Hello, %s. You are %s." % (name, age)

    注:这种格式不是很好,因为它是冗长的,会导致错误。

    二、str.format()

    str.format() 在Python 2.6中引入的。

    (1)使用str.format(),替换字段用大括号标记:

    "Hello, {}. You are {}.".format(name, age)
    # 输出结果:'Hello, Eric. You are 74.'

    (2)可以通过引用其索引来以任何顺序引用变量:

    "Hello, {1}. You are {0}-{0}.".format(age, name)
    # 输出结果:'Hello, Eric. You are 74-74.'

    (3)如果插入变量名称,则会获得额外的能够传递对象的权限,然后在大括号之间引用参数和方法:

    person = {'name': 'Eric', 'age': 74}
    "Hello, {name}. You are {age}.".format(name=person['name'], age=person['age'])
    # 输出结果:'Hello, Eric. You are 74.'

    (4)可以使用**来用字典来完成这个巧妙的技巧:

    person = {'name': 'Eric', 'age': 74}
    "Hello, {name}. You are {age}.".format(**person)
    # 输出结果:'Hello, Eric. You are 74.'

    注:当处理多个参数和更长的字符串时,str.format()仍然可能非常冗长。

    三、f-Strings

    f-Strings是在Python 3.6开始加入标准库。也称为“格式化字符串文字”,F字符串是开头有一个f的字符串文字,以及包含表达式的大括号将被其值替换。

    (1)f-Strings

    name = "Eric"
    age = 74
    f"Hello, {name}. You are {age}."
    # 输出结果:'Hello, Eric. You are 74.'

    (2)用大写字母F也是有效的:

    name = "Eric"
    age = 74
    F"Hello, {name}. You are {age}."
    # 输出结果:'Hello, Eric. You are 74.'

    (3)可以调用函数

    name = "Eric"
    age = 74
    f"{name.lower()} is funny."
    # 输出结果:'eric is funny.'
    
    f"{2 * 37}"
    # 输出结果:'74'

    (4)可以使用带有f字符串的类创建对象

    class Comedian:
        def __init__(self, first_name, last_name, age):
            self.first_name = first_name
            self.last_name = last_name
            self.age = age
        def __str__(self):
            return f"{self.first_name} {self.last_name} is {self.age}."
        def __repr__(self):
            return f"{self.first_name} {self.last_name} is {self.age}. Surprise!"
    
    new_comedian = Comedian("Eric", "Idle", "74")
    f"{new_comedian}"
    # 输出结果;'Eric Idle is 74.'
    
    f"{new_comedian!r}"
    # 输出结果:'Eric Idle is 74. Surprise!'

    (5)多行f-string

    message = (f"Hi {name}. "
            f"You are a {profession}. "
            f"You were in {affiliation}.")
    # 输出结果:'Hi Eric. You are a comedian. You were in Monty Python.'
    
    message = (f"Hi {name}. "
            "You are a {profession}. "
            "You were in {affiliation}.")
    # 输出结果:'Hi Eric. You are a {profession}. You were in {affiliation}.'

    (6)使用"""

    message = f"""
        Hi {name}. 
        You are a {profession}. 
        You were in {affiliation}.
     """
    # 输出结果:'
        Hi Eric. 
        You are a comedian. 
        You were in Monty Python.
     '

    (7)性能

    f字符串中的f也可以代表“速度快”。f-字符串是运行时渲染的表达式,而不是常量值。

    速度比较:

    %%timeit
    name = "Eric" 
    age = 74 
    '%s is %s.' % (name, age)
    # 202 ns ± 2.05 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
    
    %%timeit
    name = "Eric" 
    age = 74 
    '{} is {}.'.format(name, age)
    # 244 ns ± 5.52 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
    
    %%timeit
    name = "Eric" 
    age = 74 
    '{name} is {age}.'
    # 14.4 ns ± 0.0121 ns per loop (mean ± std. dev. of 7 runs, 100000000 loops each)

    (8)语法正确格式

    f"{'Eric Idle'}"
    # 输出结果:'Eric Idle'
    f'{"Eric Idle"}'
    # 输出结果:'Eric Idle'
    f"""Eric Idle"""
    # 输出结果:'Eric Idle'
    f'''Eric Idle'''
    # 输出结果:'Eric Idle'
    f"The "comedian<span class="string">" is {name}, aged {age}."
    # 输出结果:'The "comedian" is Eric, aged 74.'

    (9)字典

    字典的键使用单引号,请记住确保对包含键的f字符串使用双引号。

    comedian = {'name': 'Eric Idle', 'age': 74}
    f"The comedian is {comedian['name']}, aged {comedian['age']}."
    # 输出结果:'The comedian is Eric Idle, aged 74.'

    (10)大括号

    为了使字符串出现大括号,您必须使用双大括号:

    f"{{74}}"
    # 输出结果:'{74}'
    
    f"{{{{74}}}}"
    # 输出结果:'{{74}}'
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  • 原文地址:https://www.cnblogs.com/lizm166/p/10267105.html
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