python中format的用法实例详解

s = "{} is a {}".format('Tom', 'Boy')
print(s) # Tom is a Boy

s1 = "{} is a {}".format('Tom')
# 抛出异常， Replacement index 1 out of range for positional args tuple
print(s1)

s = "{0} is a {1}".format('Tom', 'Boy')
print(s) # Tom is a Boy

s1 = "{1} is a {2}".format('Tom', 'Lily', 'Girl')
print(s1) # Lily is a Girl

s = "{1} is a {0}".format('Boy', 'Tom', )
print(s) # Tom is a Boy

s = "{name} is a {sex}".format(name='Tom', sex='Boy')
print(s) # Tom is a Boy

name = 'Tom'
sex = 'Girl'
# 以f开头表示在字符串中支持大括号内的python表达式   此用法3.6之后支持
s = f"{name} is a {sex}"
print(s) # Tom is a Boy

s = "My name is {}, i am {age} year old, She name is {}".format('Liming', 'Lily', age=10)
print(s) # My name is Liming, i am 10 year old, She name is Lily

s = "My name is {}, i am {age} year old, She name is {}".format('Liming', age=10, 'Lily')
print(s)  # SyntaxError: positional argument follows keyword argument

s = "{} is a {0}".format('Boy', 'Tom', )
print(s)

s1 = "{} is a {1}".format('Boy', 'Tom', )
print(s1)

#以上两种写法均报异常。
# ValueError: cannot switch from automatic field numbering to manual field specification

class Names():
    name1='Kevin'
    name2='Tom'
print 'hello {names.name1} i am {names.name2}'.format(names=Names) 
# hello Kevin i am Tom

s = "The word is {s}, {s[0]} is initials".format(s='world')
# The word is world, w is initials
print(s)

s = 'π is {:.2f}'.format(3.1415926)
print(s) # π is 3.14

s1 = 'π is %.2f'% 3.1415926
print(s1) # π is 3.14

s = "{:.1}".format('Hello')
print(s) # H 

s = "{:,}".format(1000000)
print(s) # 1,000,000

s = "{:b}".format(8)
print(s) # 1000

s = "{:o}".format(8)
print(s) # 10

s = "{:X}".format(12)
print(s) # C

s = "{:2}b".format('a')
print(s) # a b  (a后面补了一个空格)
# 如果指定的长度小于参数的长度，按照原参数匹配
s1 = "{:2}World".format('Hello')
print(s1) # HelloWorld

s = "{:*^10}".format('Hello')
print(s) # **Hello***

s = "{:-^20}".format('123456')
print(s) # -------123456-------

s = "{:*^3}".format('Hello')
print(s) # Hello

foods = ['fish', 'beef', 'fruit']
s = 'i like eat {} and {} and {}'.format(*foods)
# i like eat fish and beef and fruit
print(s)

foods = ['fish', 'beef', 'fruit']
s = 'i like eat {2} and {0} and {1}'.format(*foods)
# i like eat fruit and fish and beef
print(s)

dict_temp = {'name': 'Lily', 'age': 18} 
# 字典需要用 ** 进行拆分
s = 'My name is {name}, i am {age} years old'.format(**dict_temp)
print(s) # My name is Lily, i am 18 years old