一文了解python 3 字符串格式化 F-string 用法

In [1]: name='Eric'

In [2]: 'Hello,%s'%name

Out[2]: 'Hello,Eric'

In [3]: name='Eric'

In [4]: age=18

In [5]: 'Hello %s,you are %d.'%(name,age)

Out[5]: 'Hello Eric,you are 18.'

In [6]: first_name = "Eric"
 ...: last_name = "Idle"
 ...: age = 74
 ...: profession = "comedian"
 ...: affiliation = "Monty Python"


In [7]: "Hello, %s %s. You are %s. You are a %s. You were a member of %s." % (first_name, last_name, age, profession, affiliation)

Out[7]: 'Hello, Eric Idle. You are 74. You are a comedian. You were a member of Monty Python.'

In [8]: 'hello,{}. You are {}.'.format(name,age)

Out[8]: 'hello,Eric. You are 74.'

In [9]: 'hello,{1}. You are {0}.'.format(age,name)

Out[9]: 'hello,Eric. You are 74.'

In [10]: person={'name':'Eric','age':74}

In [11]: 'hello,{name}. you are {age}'.format(name=person['name'],age=person['age'])

Out[11]: 'hello,Eric. you are 74'

In [15]: 'hello,{name}. you are {age}'.format(**person)

Out[15]: 'hello,Eric. you are 74'

>>> first_name = "Eric"

>>> last_name = "Idle"

>>> age = 74

>>> profession = "comedian"

>>> affiliation = "Monty Python"

>>> print(("Hello, {first_name} {last_name}. You are {age}. " +

>>>  "You are a {profession}. You were a member of {affiliation}.") \

>>>  .format(first_name=first_name, last_name=last_name, age=age, \

>>>    profession=profession, affiliation=affiliation))
'Hello, Eric Idle. You are 74. You are a comedian. You were a member of Monty Python.'

In [16]: name = 'Eric'

In [17]: age=74

In [18]: f'hello {name}, you are {age}'

Out[18]: 'hello Eric, you are 74'

In [19]: F'hello {name}, you are {age}'

Out[19]: 'hello Eric, you are 74'

In [20]: f'{2*37}'

Out[20]: '74'

In [22]: def to_lowercase(input):
 ...:  return input.lower()
 ...:

In [23]: name = 'ERIC IDLE'

In [24]: f'{to_lowercase(name)} is funny'

Out[24]: 'eric idle is funny'

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}"'Eric Idle is 74.'

>>> f"{new_comedian}"
'Eric Idle is 74.'

>>> f"{new_comedian!r}"
'Eric Idle is 74. Surprise!'

>>> name = "Eric"

>>> profession = "comedian"

>>> affiliation = "Monty Python"

>>> message = (
...  f"Hi {name}. "
...  f"You are a {profession}. "
...  f"You were in {affiliation}."
... )

>>> message
'Hi Eric. You are a comedian. You were in Monty Python.'

>>> message = f"Hi {name}. " \
...   f"You are a {profession}. " \
...   f"You were in {affiliation}."...

>>> message
'Hi Eric. You are a comedian. You were in Monty Python.'

>>> message = f"""
...  Hi {name}. 
...  You are a {profession}. 
...  You were in {affiliation}.
... """
...

>>> message
'\n Hi Eric.\n You are a comedian.\n You were in Monty Python.\n'

import timeit

time1 = timeit.timeit("""name = 'Eric'\nage =74\n'%s is %s'%(name,age)""",number=100000)
time2 = timeit.timeit("""name = 'Eric'\nage =74\n'{} is {}'.format(name,age)""",number=100000)
time3 = timeit.timeit("""name = 'Eric'\nage =74\nf'{name} is {age}'""",number=100000)

0.030868000000000007
0.03721939999999996
0.0173276

f"{'Eric Idle'}"
f'{"Eric Idle"}'
f"""Eric Idle"""
f'''Eric Idle'''

>>> comedian = {'name': 'Eric Idle', 'age': 74}

>>> f"The comedian is {comedian['name']}, aged {comedian['age']}."

>>> f'The comedian is {comedian['name']}, aged {comedian['age']}.'

>>> f"{{74}}"'{74}'

>>> f"{{{{74}}}}"

>>> f"{\"Eric Idle\"}"
 File "<stdin>", line 1
 f"{\"Eric Idle\"}"
      ^SyntaxError: f-string expression part cannot include a backslash

>>> name = "Eric Idle"

>>> f"{name}"'Eric Idle'