python如何正確的操作字符串

>>> "Hello world!"
'Hello world!'

>>> 'Hello  world!'
'Hello  world!'

>>> "Let's go!"
"Let's go!"

>>> 'she said "Hello world!" '
'she said "Hello, world!" '

>>> 'Let\'s go!'
"Let's go!"

>>> "\"Hello, world!\" she said"
'"Hello, world!" she said'

>>> "she said " + '"Hello world!"'
'she said "Hello world!"'

>>> a = "she said "
>>> b = '"Hello world!"'
>>> a + b
'she said "Hello world!"'

>>> "she said " '"Hello world!"'   
'she said "Hello world!"'

# 只有輸入的是字符串才有用
>>> a = "she said "
>>> b = '"Hello world!"'
>>> a  b
  File "stdin>", line 1
    a  b
       ^
SyntaxError: invalid syntax

>>> """like this"""
'like this'

>>> print('''long long ago!
"Hello world!"
she said.''')
long long ago!
"Hello world!"
she said. 

>>> 1 + 2 + 

4 + 5
12

>>> print("Hello  \

 world!")
Hello  world!

>>> print 

('Hello  world')
Hello  world

>>> 'Hello'[1]
'e'

>>> yearnum = input('please input year: ')[3]
please input year: 2021
>>> yearnum
'1'  

>>> 'python' * 3 
'pythonpythonpython'

>>> access_mode = 'rw+'
>>> 'w' in access_mode 
True
>>> 'x' in access_mode 
False

>>> subject = '$$$ Get rich now!!! $$$'
>>> '$$$' in subject 
True

>>> somelist = list('Hello')
>>> somelist
['H', 'e', 'l', 'l', 'o']

>>>''.join(somelist)

>>> name = list('Perl')
>>> name 
['P', 'e', 'r', 'l']

>>> name[2:] = list('ar')
>>> name 
['P', 'e', 'a', 'r']

>>> name = list('Perl')
>>> name[1:] = list('ython')
>>> name 
['P', 'y', 't', 'h', 'o', 'n']

>>> format = "Hello, %s. %s !"
>>> values = ('world', 'python')
>>> format % values 
'Hello, world. python !'

>>> from string import Template
>>> tmpl = Template("Hello, $param1! $param2 !")
>>> tmpl.substitute(param1="world", param2="Python") 
'Hello, world! Python !'

>>> "{}, {} and {}".format("first", "second", "third") 
'first, second and third'
>>> "{0}, {1} and {2}".format("first", "second", "third") 
'first, second and third'
>>> "{3} {0} {2} {1} {3} {0}".format("be", "not", "or", "to") 
'to be or not to be'

>>> from math import pi
>>> "{name} 約等于 {value:.2f}.".format(value=pi, name="π") 
'π 約等于 3.14.''

>>> from math import e
>>> f"Euler's constant is roughly {e}."  # 等價(jià)于 "Euler's constant is roughly {e}.".format(e=e)
"Euler's constant is roughly 2.718281828459045."

>>> "{foo} {} {bar} {}".format(1, 2, bar=4, foo=3)
 '3 1 4 2'

>>> "{foo} {1} {bar} {0}".format(1, 2, bar=4, foo=3) 
'3 2 4 1'

>>> fullname = ["Alfred", "Smoketoomuch"]
>>> "Mr {name[1]}".format(name=fullname) 
'Mr Smoketoomuch'

>>> import math
>>> tmpl = "The {mod.__name__} module defines the value {mod.pi} for π"
>>> tmpl.format(mod=math) 
'The math module defines the value 3.141592653589793 for π'

>>> print("{pi!s} {pi!r} {pi!a}".format(pi="π")) 
π 'π' 'u03c0'

>>> "The number is {num}".format(num=42) 
'The number is 42'
>>> "The number is {num:f}".format(num=42) 
'The number is 42.000000'
>>> "The number is {num:b}".format(num=42) 
'The number is 101010'

>>> seq = ['1', '2', '3', '4', '5']
>>> sep = '+'
>>> sep.join('+') # 合并一個(gè)字符串列表
'1+2+3+4+5'

>>> '1+2+3+4+5'.split('+')
['1', '2', '3', '4', '5']
>>> 'Using the default'.split()
['Using', 'the', 'default']