The most understandable f-string tutorial in history, collecting this one is enough

One 、 Preface

Following %、format After the formatting ,Python 3.6 Began to introduce a more efficient string formatting ：f-string.

f-string In form f Modifier LED string （f''）, In the string {} Indicates the field to be replaced .f-string In essence, it is not a string constant , It's an expression that evaluates at run time .

Two 、 Basic operation

f-string Medium {} Represents the field to be replaced , Here's an example

"""  Comparison of three ways of formatting strings  """
name = 'raelum'
print('%s' % name)
# raelum
print('{}'.format(name))
# raelum
print(f'{
      name}')
# raelum

As I said before ,{} in What is actually stored is the value of the expression , This means that we can be in {} Carry out operations ：

name = 'raelum'
print(f'{
      name.upper()}')
# RAELUM
print(f'{
      name + name.capitalize()}')
# raelumRaelum
print(f'{
      name[:-1]}')
# raelu

"""  More examples   One """
print(f'{
      2 * 3 + 5}')
# 11
print(f'{
      sum([i for i in range(10)])}')
# 45
print(f'{
      [i ** 2 for i in range(3)]}')
# [0, 1, 4]

"""  More examples   Two """
name = 'Li Hua'
num = 13
print(f'My name is {
      name}.')
# My name is Li Hua.
print(f'I have {
      num} apples.')
# I have 13 apples.

3、 ... and 、 Quotation mark specification

f-string in {} Quotation marks used inside cannot be compared with {} The quotation mark delimiter outside conflicts , That is, the following operations are not allowed ：

print(f'My name is {'Li Hua'}')
# SyntaxError: f-string: expecting '}'

It can be output normally in any of the following forms （ All the possible situations are listed below ）：

"""  The outer delimiter is a single quotation mark  """
print(f'My name is {
      "Li Hua"}')
print(f'My name is {
      """Li Hua"""}')

"""  The outer delimiter is a double quotation mark  """
print(f"My name is {
      'Li Hua'}")
print(f"My name is {
      '''Li Hua'''}")

"""  The outer delimiter is double three quotation marks  """
print(f"""My name is {
      'Li Hua'}""")
print(f"""My name is {
      "Li Hua"}""")
print(f"""My name is {
      '''Li Hua'''}""")

"""  The outer delimiter is a single three quotation mark  """
print(f'''My name is {
      'Li Hua'}''')
print(f'''My name is {
      "Li Hua"}''')
print(f'''My name is {
      """Li Hua"""}''')

summary ： If there are many kinds of quotation marks inside the string, but you don't want to worry about quotation marks , External delimiters are used directly """ That's it .

Four 、 The problem of escape

f-string Can't be in {} Internal use escape , But in {} Escape outside , as follows ：

print(f"{
      '\''}")
# SyntaxError: f-string expression part cannot include a backslash
print(f"\'")
# '

If it really needs to be in {} Use the escape , Should contain \ The content of is declared as a variable separately

s = '\''
print(f"{
      s}")
# '

5、 ... and 、 alignment

f-string Of {} Used in content:format To set the string format , To use the default format , You don't have to specify :format.

5.1 By default, spaces are used to fill

name = 'raelum'
print(f'{
      name:>20}')  #  Right alignment , Fill string length to 20
# raelum
print(f'{
      name:<20}')  #  Align left , Fill string length to 20
# raelum 
print(f'{
      name:^20}')  #  Align center , Fill string length to 20
# raelum 

5.2 Fill with other characters

name = 'raelum'
print(f'{
      name:a>20}')
# aaaaaaaaaaaaaaraelum
print(f'{
      name:1<20}')
# raelum11111111111111
print(f'{
      name:-^20}')
# -------raelum-------

6、 ... and 、 Width and precision

Format descriptor	effect
width	Integers width Specify the width
0width	Integers width Specify the width ,0 For high order, use 0 Make up width
width.precision	Integers width Specify the width ,precision Specify the precision

When given precision when ,width Omission .

import numpy as np

"""  Example 1  """
a = 123456
print(f'{
      a:4}')
# 123456
print(f'{
      a:8}')
# 123456
print(f'{
      a:08}')
# 00123456

"""  Example 2  """
b = np.pi
print(f'{
      b:.3f}')
# 3.142
print(f'{
      b:8.3f}')
# 3.142
print(f'{
      b:08.3f}')
# 0003.142

Last

This article only introduces f-string Some of the most commonly used operations in , To learn more , You can go to Official documents Further study .