Python String formatting

• 1. % Format characters
• • 1.1） Common format characters
• 2. format()
• • 2.1） Use location
  • 2.2） Use a custom parameter name
  • 2.3） Unpack with sequence
  • 2.4） Format style
• 3. map
• 4. f- character string

String formatting Used to convert integers 、 Objects such as real numbers are converted to strings in a specific format

1. % Format characters

% Format characters ：% The previous string is the format string , The next part is the content to be formatted .

for example ：

name = "cspsy"
job = "student"
print("My name is %s." % name)
# If there is more than one content that needs to be formatted , Need to use () Wrap it in .
print("My name is %s and my job is %s." % (name, job))

1.1） Common format characters

2. format()

format()： .format() The previous string is the format string , The contents of the inner part are the contents that need to be formatted .
In the format string {} The content and content of format() The contents inside correspond to .

format() Method to format ：

• Sure Use location format
• Sure Use a custom parameter name format
• Support sequence unpacking To format

2.1） Use location

• Do not write position subscript , Then the subscript of the curly bracket in the format string defaults from 0 Start incremental arrangement

name = "cspsy"
job = "student"
print("My name is {} and my job is {}.".format(name, job))

• Writing position subscript , Output the contents of the subscript at the specified position in parentheses （ The subscript in brackets is from 0 Start incremental arrangement ）

one, two, three = 1, 2, 3
print("You use {0}, {2}, {1}.".format(one, two, three))

2.2） Use a custom parameter name

• It can be found in the format string {} The user-defined parameter name is used in the , Corresponding to the content to be formatted .
  for example ：

one, two, three = 1, 2, 3
print("You use {o}, {thr}, {tw}.".format(o=one, tw=two, thr=three))

2.3） Unpack with sequence

Will unpack the name ,key Value in the format string .
for example ：

number = {
'one': 1, 'two': 2, 'three': 3}
print("You use {one}, {three}, {two}.".format(**number))

2.4） Format style

• Numbers

Hexadecimal conversion

one, two, three = 11111, 2222, 3
print("You use {0:#x}, {1:#o}, {2:#b}".format(one, two, three))

Keep the decimal point
Use :.xf,x For the number of decimal points you want to keep , If : With +, The symbol output is preserved .

one, two, three = 11111.1111, 2.2222, 3.3333333
print("You use {0:.2f}, {1:+.0f}, {2:.3f}".format(one, two, three))

Scientific enumeration

one, two, three = 11111.1111, 2.2222, 3.3333333
print("You use {0:.2e}, {1:+.0e}, {2:.3e}".format(one, two, three))

Percentage form

one, two, three = 11111.1111, 2.2222, 3.3333333
print("You use {0:.0%}, {1:.2%}, {2:.3%}".format(one, two, three))

Separated by commas

one, two, three = 11111.1111, 2.2222, 3.3333333
print("You use {0:,}, {1:,}, {2:,}".format(one, two, three))

• Alignment mode

Use :cxn To carry out ,n Is the minimum length ,c When the length is not enough , Filled characters （ If it is not written, it will be a blank space ）
x For alignment ： among ,^： In the middle ,<： Align left ,>： Right alignment

for example ：

one, two, three = 11111.1111, 2.2222, 3.3333333
print("You use {0:#^12.2f}, {1:.<+8.0f}, {2:>7.3f}".format(one, two, three))

3. map

Can be built through map() Function to format string output ：

formatter = "You use {0}".format
for num in map(formatter, range(1, 6)):
print(num)

This example is equivalent to the following ：

formatter = "You use {0}".format
for num in range(1, 6):
print(formatter(num))

4. f- character string

from Python 3.6.x Start to support a new format for Strings , The official name is Formatted String Literals, abbreviation f- character string , Prefix the string with a letter f, stay {} in Fill in the expression .
Use as follows ：

one, two, three = 11, 222, 3333
print(f'You use {
one}, {
two * three}.')

Python 3.8 after , just so so {xxx=}, take xxx= Output and output its corresponding value ：

one, two, three = 1, 2, 3
print(f'You use {
one}, {
two * three}, {
two * three = }.')