2.7 format output of values

It mainly introduces the common format output of various data types .

1） Let's first look at the problem of integers , That is, the formatted display of different base numbers . For example, for decimal integers , Whether it can be displayed in other base numbers ？

Let's first look at the use print Function format function ：

num = 100
print('%x' % num)

Output is ： 64. there % The character represents the marker conversion specifier ,%x Said to 16 Hexadecimal display value , This is the old version Python Writing . We can use a more powerful new way of writing .

num = 100
print(format(num, 'b'))
print(format(num, 'o'))
print(format(num, 'x'))
print(format(num, 'd'))

Output is ：
1100100
144
64
100

This shows that using format Function to realize format conversion , And it can also be converted to other base numbers , It's all through format The second parameter is to distinguish , such as b、o、x、d Respectively represent binary 、 octal 、 Hexadecimal and decimal .

format You can also convert other base numbers to decimal ：

num = 0b100
print(format(num, 'd'))

Output is ：4.

You can also use some special functions to complete the conversion to other specific base numbers , For example, the conversion from decimal to other decimal ：

num = 100
print(bin(num))
print(oct(num))
print(hex(num))

Output is ：
0b1100100
0o144
0x64

But there is no ready-made function that can be converted to decimal function , Therefore, we can skillfully use combination to realize ：

num = 0b100
print(int(str(num), 10))

Output is ：4.

2） Let's look at the problem of floating point numbers , This paper mainly introduces the format conversion of scientific counting .

  For example, decimal conversion to scientific counting ：

num = 1 / 3
print('{:.4e}'.format(num))

Output is ：
3.3333e-01

among 4 It can be replaced as appropriate , there 4 Express 4 For decimal places . Whole {:.4e} It is an output format of scientific counting . It can also be written in another old version with the same effect ：

num = 1 / 3
print('%.4e' % num)

The output content is the same as .

In turn, , Scientific counting method can also be converted to normal decimal form ：

num = 3.3333e-01
print('{:.3f}'.format(num))

Output is ：
0.333

Please pay attention to e Instead of f The difference between .

You can also use the old version ：

num = 3.3333e-01
print('%.3f' % num)

The output content is the same as .

3） Finally, let's look at the formatted output of the string .

The formatted output content of string is the most diverse , It is also the most practical . Let's illustrate with a few examples . Let's first look at the output of formatted variable values . This is the most primitive method , Directly use the plus sign to connect the string to form the required output format and content ：

strs = ' nanjing '
print(' The value of the variable is ' + strs)

Output is ： The value of the variable is Nanjing

You can also use format Format ：

strs = ' nanjing '
print(' The value of the variable is {}'.format(strs))

The output content is the same as .print Curly braces for parameters in function {} Represents a placeholder , It can be understood as an empty , wait for format Function parameter variable value to fill . And even other data types can ：

num = 1
print(' The value of the variable is {}'.format(num))

Output is ：
The value of the variable is 1

Obviously, if so + How to write it , You also need to convert data types , Therefore, this writing method is simpler .

For multiple variables , Still convenient ：

strs1 = ' nanjing '
strs2 = ' jiangsu '
print('{} yes {} The provincial capital, '.format(strs1, strs2))

Output is ：
Nanjing is the capital of Jiangsu Province

You can also write like this ：

strs1 = ' nanjing '
strs2 = ' jiangsu '
print(f'{strs1} yes {strs2} The provincial capital, ')

The output content is the same as ,f The prefix indicates that what is in all curly braces is the corresponding variable to be output .

You can also use % Form placeholders achieve the same effect , Such as %s Representation string ：

strs1 = ' nanjing '
strs2 = ' jiangsu '
print('%s yes %s The provincial capital, ' % (strs1, strs2))

The output content is the same as . We will use some later exercises format Function other format usage , At that time, we will learn and use .
 

Supporting learning resources 、 MOOC video ：

Python Big data analysis - Shu Qing Li https://www.njcie.com/python/