Usage Summary of str.format() function [not 'str****{}'.Format()]

Catalog

One 、 The cause of the article

Two 、str.format(self,*args)

3、 ... and 、 Main stream print expression

3.1 print('**%f**' %x)

3.2 print(f'**{xx}**')

3.3 print(***{}***.format(*args)

Four 、format stand on one 's own 、 Get rid of print,“ Realize output freedom ”

5、 ... and 、 Reference source

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One 、 The cause of the article

Because I am using 《 Deep learning - Case based understanding of deep neural networks 》 When studying , The code given by the author is similar to the following

# Input 
cost = 6.512345
print(str.format(' The result value of the cost function ={0:.6f}', cost))

# Output 
 The result value of the cost function =6.512345

Then I search on Baidu Google 「str.format」 Usage of , All you get is to put the body of the string in format Usage outside

print('{} {}'.format('hello','world'))  #  Without fields 
hello world
print('{0} {1}'.format('hello','world'))  #  Numbered number 
hello world
print('{0} {1} {0}'.format('hello','world'))  #  Out of order 
hello world hello
print('{1} {1} {0}'.format('hello','world'))
world world hello

So I have to study it again and again , Then it is summarized as follows .

Two 、str.format(self,*args)

Private opinion ,str.format(self,*args) yes format A high-level expression of a function . It seems that if you use this method , Only one can be used to replace , Multiple substitutions will say that the parameter field is exceeded .

print('hello,world,I am {} {} {}'.format(' Small ',' bad ',' egg ')  #  Actual string substitution str

print(str.format('hello,world,I am {}',[' Little villain ']))  # utilize str Under class format Function output string 

print(str.format('hello,world,my number is {:.6f}', 8.888))


# Output results 
hello,world,I am  Small   bad   egg 

hello,world,I am  Little villain 

hello,world,my number is 8.888000


# Wrong expression 
print(str.format('hello,world,I am {} {} {}',[' Small ',' bad ',' egg ']) # It seems that only one parameter can be inserted into str in 
#IndexError: Replacement index 1 out of range for positional args tuple

3、 ... and 、 Main stream print expression

3.1 print('**%f**' %x)

print('This is a number equal to %f' %1.11)
# This is a number equal to 1.110000

 What if you want to output multiple variables ？ In parentheses ！
print('This is a number equal to %f, instead of %d' %(1.11,1))
#This is a number equal to 1.110000, instead of 1

3.2 print(f'**{xx}**')

That is to say 「 Abbreviation f Put it in print front 」. As shown in the following code block .

Be careful ： such f Method , Only one single quotation mark or double quotation mark can be followed , Can't be in f When you add double quotation marks, you also {} Put double quotation marks inside , Nor in f When you add a single quotation mark, you will also {} Put single quotation marks in it .

#  Output number （ Integers 、 floating-point 、 The plural ）, Direct output , No quotes 
print(f'Hello world, I am No.{1}')  #  Direct output Hello world, I am No.1
one = 1
print(f'Hello world, I am No.{one}')  #  Indirect output Hello world, I am No.1

#  Direct output string , If f Single quotation mark after , Be sure to use double quotation marks in curly braces 
print(f'Hello world, I am {" Little villain "}.')  # Hello world, I am  Little villain .
print(f'Hello world, I am {' Little villain '}.')  # SyntaxError: invalid syntax

#  Or in f Double quotation mark after , You can put single quotation marks in the replacement part of the string 
print(f"Hello world, I am {' Little villain '}.")  # Hello world, I am  Little villain .

#  Use variables to output strings indirectly , You don't need quotation marks 
y = ' Little villain '
print(f'Hello world, I am {y}.')  # Hello world, I am  Little villain .

3.3 print(***{}***.format(*args)

（1） If the curly braces contain nothing , Is to replace by position

（2） If it is replaced by serial number , You can rearrange the order . And if the element is a sequence （ list 、 Tuples 、 Dictionary, etc ）, Or the plural , You can also replace its sub content （ The sub content of a complex number includes its real part and imaginary part , The sub contents of a list are the elements of its dimensions , The child content of a class is its variables or functions ）.

print(' The real part of a complex number ={0.real}, Imaginary part ={0.imag}'.format(1+2j)) 
# The real part of a complex number =1.0, Imaginary part =2.0

print(' A sub content of the list is {0[1][1]}'.format([[1,2],[1,2]]))
#  A sub content of the list is 2

（3） Empathy , Replace by keyword , It can also be placed out of order .

（4） In an output body , Can include both 「 Replace by position 」 and 「 Replace by serial number 」.

print('{} {}'.format('hello','world'))  #  Without fields 
hello world
print('{0} {1}'.format('hello','world'))  #  Numbered number 
hello world
print('{0} {1} {0}'.format('hello','world'))  #  Out of order 
hello world hello
print('{1} {1} {0}'.format('hello','world'))
world world hello
print('{a} {tom} {a}'.format(tom='hello',a='world'))  #  With the keyword 
world hello world

Four 、format stand on one 's own 、 Get rid of print,“ Realize output freedom ”

It seems that most of the output with strings , You have to use print function , But the following expression , But you can avoid print monopoly , Achieve independent output freedom .

Empathy ： Nor in f Back 、{} Use double or single quotation marks inside .

But this method has some defects , That is, the output string has single quotation marks .

The road to independence is hard 、 Questionable , however , We must believe —— Just stick to it , We will certainly catch up with the international advanced level ！ Pay tribute to ！！！

#  The path of independence 1：a.format(b)

"{0} {1}".format("hello","world")
#'hello world'
 
 
#  The path of independence 2：f"xxxx" or f'xxxx'

f"{'hello'} {'world'}"
 or 
f'{"hello"} {"world"}'

# The output is 'hello world'

5、 ... and 、 Reference source

 python print（% Usage and format usage ）_wjqhit The column -CSDN Blog _print

python Of print(f‘)_wuli_xin The blog of -CSDN Blog _python in print(f)