How to use python's format function

What you can do with the format function

[You can substitute the value / string defined by the argument](# 1 Substitute the value string defined by the argument)
[Multiple arguments can be set](Specify multiple values for # 2 argument)
[Specify by index number](#Specify by presence or absence of index number)
[Can use the same argument multiple times](#Call multiple times)
[Same order](when there are multiple # arguments)
[Can be set with character string / numerical value / variable](# 3 Set with character string numerical variable)
[Wide width](# 4 Widen width)
[Left-justified, right-justified, center-justified](# 5 Specify text alignment align)
[Fill in blanks](# 7 Fill in blanks)
[Fill with zero](#Fill with zero)
[Fill with any character](#Fill with any character)
[Set comma in thousands](# Set comma in thousands)
[Display% (100 times numerical value)](# 8 100 times numerical value displayed)
[Add a sign to the number](# 9 Add a sign to the number)
[Specify the number of decimal places](# 10 Specify the number of decimal places)
[Fixed-point notation (e)](# 11 Fixed-point notation e)
[Specify variable in argument](# 12 Specify variable in argument)
[Convert date data to specified character string](# 13 Convert date data to specified character string)

## How to use the format function ### (1) Substitute the value / character string defined in the argument ** Basic syntax ** `{}.format(A)` └ The contents of A are in {}

`Example (basic form)`


'{}The weather at the station is sunny'.format('Shibuya')

#output
#'The weather at Shibuya station is sunny'

### (2) Specify multiple values for the argument `{n}.format(A,B,C,,,)` └ n: Specify the argument number (number) (from 0) └ 0 if no number is specified

Designation by presence / absence of index number

`Example (no index number)`


'{}The weather at the station is sunny'.format('Shibuya','Shinjuku','Mejiro','Ikebukuro')

#output
#'The weather at Shibuya station is sunny'

`Example (index number 0)`


'{0}The weather at the station is sunny'.format('Shibuya','Shinjuku','Mejiro','Ikebukuro')

#output
#'The weather at Shibuya station is sunny'

`Example (index number 1)`


'{1}The weather at the station is sunny'.format('Shibuya','Shinjuku','Mejiro','Ikebukuro')

#output
#'The weather at Shinjuku station is sunny'

`Example (index number 4)`


'{4}The weather at the station is sunny'.format('Shibuya','Shinjuku','Mejiro','Ikebukuro')

#output(error)
#IndexError: Replacement index 4 out of range for positional args tuple

If there is no data corresponding to the index number, an error will occur.

### Call multiple times #### One argument `{0}{0}{0},,,.format(A)` └ The argument value is entered in the installed {0}

`Example (call one argument multiple times)`


'{0}Weather.{0}Ward,{0}The weather at the station is sunny'.format('Shibuya')

#output
#'Shibuya weather. The weather at Shibuya Ward and Shibuya Station is sunny'

If 0 is not specified for the index number, an error will occur. Because the index number in {} is automatically set in order from 0.

`Example (error case)`


'{}Weather.{}Ward,{}The weather at the station is sunny'.format('Shibuya')

#output(error)
#IndexError: Replacement index 1 out of range for positional args tuple

#### When there are multiple arguments

`Example (multiple arguments, no number specified)`


'{}Weather.{}Ward,{}The weather at the station is sunny'.format('AAAA','BBBB','CCCC','DDDD')

#output
#'AAAA weather. The weather at BBBB Ward and CCCC Station is sunny'

Index number is set automatically --First {} = {0} --Second {} = {1} --Third {} = {2} ・・・

`Example (multiple arguments, number specified ①)`


'{0}Weather.{1}Ward,{2}The weather at the station is sunny'.format('AAAA','BBBB','CCCC','DDDD')

#output
#'AAAA weather. The weather at BBBB Ward and CCCC Station is sunny'

The result is the same as without a number.

`Example (multiple arguments, number specified ②)`


'{3}Weather.{2}Ward,{2}The weather at the station is sunny'.format('AAAA','BBBB','CCCC','DDDD')

#output
#'DDDD weather. The weather at CCCC Ward and CCCC Station is sunny'

・ In no particular order ・ The same number can be set multiple times

### (3) Set with character strings, numbers, and variables

`Example (set by character string, numerical value, variable)`


mountain = 'Mt. Kitadake'
altitude = '3193'

'{}so{}The highest mountain{}.. The altitude is{}m'.format('Japan',2,mountain,altitude)

#output
#'The second highest mountain in Japan is Mt. Kitadake. Altitude is 3193m'

・ Character string: Japan ・ Numerical value: 2 -Variable (character string): mountain ・ Variable (numerical value): altitude

### (4) Widen the width (width) `{:n}.format()` └ Formatting below ":" └ "n" 0 or more integers └ The unit is bytes └ The minimum width is the number of bytes of the argument

`Example (width setting)`


'{:2}Set gap in format'.format('A')

#output"'Set the gap in A format'」

-Argument "A": 1 byte -Width setting: 2 bytes ⇒ 2 bytes wide (1 byte gap)

`Example (width setting "argument is larger")`


'{:2}Set gap in format'.format('AAAAA')

#output"'Set gaps in AAAAA format'」

-Argument "AAAAA": 5 bytes -Width setting: 2 bytes ⇒ 5 bytes wide

`Example (width setting "width 0")`


'{:0}Set gap in format'.format('A')

#output(error)
#「ValueError: '=' alignment not allowed in string format specifier」

### (5) Specifying text alignment (align)

symbol	Placement
<	Left justified
^	Centered
>	Right justified

** How to use ** {<n}.format() └ "<": Left justified. a line sign └ "n": width (integer greater than or equal to 0)

`Example (left justified)`


'{:<10}Set gap in format'.format('AAA')

#output
#「'Set gaps in AAA format'」

`Example (centered)`


'{:^10}Set gap in format'.format('AAA')

#output
#「'Set gaps in AAA format'」

`Example (right justified)`


'{:>10}Set gap in format'.format('AAA')

#output
#「'Set gaps in AAA format'」

`Example (set the placement individually)`


'The first one"{:<7}". The second "{:^7}". Third "{:>7}」'.format('AAA','BBB',333)

#output
#　'The first is "AAA". The second "BBB". The third "333"'

### (7) Fill in the blanks It is necessary to specify the arrangement.

Fill with zero

{0<n}.format() └ "0": Fill with 0 └ "<": Left justified. Placement specification

`Fill with zero(Left justified)`


'「{:0<10}Fill the gap with zero'.format('AAA')

#output
#　'"AAA0000000" Fill the gap with zero'

`Fill with zero(Centered)`


'「{:0^10}Fill the gap with zero'.format('AAA')

#output
#　'"000AAA0000" Fill the gap with zero'

If the gap is odd, there will be more behind.

`Fill with zero(Right justified)`


'「{:0>10}Fill the gap with zero'.format('AAA')

#output
#　'"0000000 AAA" Fill the gap with zero'

#### Fill with arbitrary characters `{@・ Only one digit can be filled ・ Both half-width and full-width are acceptable ・ Error for 2 digits or more

`@Fill with(Left justified)`


'「{:@<10}Fill the gap'.format('AAA')

#output
#　'「AAA@@@@@@@Fill the gap'

`Fill with ★(Centered)`


'「{:★^10}Fill the gap'.format('AAA')

#output
#　'"★★★ AAA ★★★★" Fill the gap'

`Fill with the number 5(Right justified)`


'「{:5<10}Fill the gap with zero'.format('AAA')

#output
#　'"AAA555 5555" Fill the gap with zero'

`Character string of 2 digits or more (error)`


'「{:★★^10}Fill the gap with zero'.format('AAA')

#Output (error)
#　ValueError: Invalid format specifier

`Two or more digits (error)`


'「{:11<10}Fill the gap with zero'.format('AAA')

#Output (error)
#　ValueError: Invalid format specifier

### (7) Set a comma in the thousands `'{:,}'.format()` └ Formatting below ":" └ "," Comma in thousands

`Example (comma in thousands)`


'{:,}'.format(123456789)

#output
#　'123,456,789'

### (8) Display% (100 times numerical value) `'{:.n%}'.format()` └ Formatting below ":" └ ".n" Number of digits after the decimal point (default 6) └ The number is multiplied by 100

`%display(Default)`


'{:%}'.format(1)

#output
#　'100.000000%'

`%display(小数点以下非display)`


'{:.0%}'.format(1)

#output
#　'100%'

`%display(2 digits after the decimal point)`


'{:.2%}'.format(1)

#output
#　'100.00%'

`%display(15 digits after the decimal point)`


'{:.15%}'.format(1)

#output
#　'100.000000000000000%'

The default of 6 digits or more can be set.

### (9) Add a + sign to the numerical value `'{:+}'.format()` └ Formatting below ":" └ Add a plus / minus sign to "+"

The default is a minus sign only. └ Same as'{:-}'(no setting required)

`Add a + sign`


'The first"{:+}". The second "{:+}". Third "{:+}」'.format(-500, 300, 2.56)

#output
#　'The first"-500 ". The second "+300 ". Third "+2.56」'

### (10) Specify the number of decimal places `'{:.nf}'.format()` └ Formatting below ":" └ ".n" Number of decimal places (integer from 0) └ Default ": .nf" None is for the input value └ Rounding

`Decimal point(Default)`


'{}'.format(1.23)

#output
#　'1.23'

`Decimal point(2 digits)`


'{:.2f}'.format(1.23456789)

#output
#　'1.23'

`Decimal point(0 digits)`


'{:.0f}'.format(1.234345678)

#output
#　'1'

`Decimal point(12 digits)`


'{:.12f}'.format(1.234345678)

#output
#　'1.234345678000'

### (11) Fixed-point notation (e) `'{:.ne}'.format()` └ Formatting below ":" └ Number of ".n" decimal points └ 6 decimal places without default ".n"

`Fixed point (default)`


'{:e}'.format(123456789)

#output
#　'1.234568e+08'

`Fixed point (2 digits)`


'{:.2e}'.format(123456789)

#output
#　'1.23e+08'

`Fixed point (no decimal point)`


'{:.0e}'.format(123456789)

#output
#　'1e+08'

`Fixed point (argument is decimal)`


'{:.0e}'.format(123.456789)

#output
#　'1e+02'

### (12) Specify a variable in the argument `'{a}{b}{c},,,'.format(a='AAA',b=111,c='CCC')` └ Specify a variable in the argument └ Cannot be specified by index number └ Cannot be used with numbers or strings

`Specify a variable in the argument`


'{a}so{b}The highest mountain{c}。'.format(a='Japan',b=2,c='Mt. Kitadake')

#output
#　'The second highest mountain in Japan is Mt. Kitadake.'

`Variables and strings are in error`


'{a}so{b}The highest mountain{2}。'.format(a='Japan',b=2,Mt. Kitadake)

#output(error)
#　SyntaxError: positional argument follows keyword argument

`Variables and numbers are errors`


'{a}so{1}The highest mountain{c}。'.format(a='Japan',2,c='Mt. Kitadake')

#output(error)
#　SyntaxError: positional argument follows keyword argument

`Cannot be specified by index number`


'{0}so{1}The highest mountain{2}。'.format(a='Japan',b=2,c='Mt. Kitadake')

#output(error)
#　IndexError: Replacement index 0 out of range for positional args tuple

`NG without index number specification`


'{}so{}The highest mountain{}。'.format(a='Japan',b=2,c='Mt. Kitadake')

#output(error)
#　IndexError: Replacement index 0 out of range for positional args tuple

### (13) Convert date data to the specified character string The date of the datetime module can be converted to the specified format (character string).

`datetime.date type`


import datetime as dt
past = dt.date(2017,1,3)

"{0:%Y year%#m month%#d day}".format(past)

#output
#　"{0:%Y year%#m month%#d day}".format(past)

`datetime.datetime type`


import datetime as dt
today = dt.datetime.now()

"{0:%Y year%m month%d day---%I time%M minutes%S seconds}".format(today)

#output
#　'March 20, 2020---02:08:39'

`Extract individually(Month and second)`


import datetime as dt
today = dt.datetime.now()

"{0:%#m month,%S seconds}".format(today)

#output
#　'March, 52 seconds'

Reference: [How to change the date format](https://qiita.com/yuta-38/items/337059e1eafab3582851#2-2format%E3%83%A1%E3%82%BD%E3%83%83] % E3% 83% 89% E3% 81% A7% E5% A4% 89% E6% 9B% B4% E3% 81% 99% E3% 82% 8B)

[Return to top](How to use the format method of #python)

[Python] Explains how to use the format function with an example

How to use python's format function

What you can do with the format function

Example (basic form)

Designation by presence / absence of index number

Example (no index number)

Example (index number 0)

Example (index number 1)

Example (index number 4)

Example (call one argument multiple times)

Example (error case)

Example (multiple arguments, no number specified)

Example (multiple arguments, number specified ①)

Example (multiple arguments, number specified ②)

Example (set by character string, numerical value, variable)

Example (width setting)

Example (width setting "argument is larger")

Example (width setting "width 0")

Example (left justified)

Example (centered)

Example (right justified)

Example (set the placement individually)

Fill with zero

Fill with zero(Left justified)

Fill with zero(Centered)

Fill with zero(Right justified)

@Fill with(Left justified)

Fill with ★(Centered)

Fill with the number 5(Right justified)

Character string of 2 digits or more (error)

Two or more digits (error)

Example (comma in thousands)

%display(Default)

%display(小数点以下非display)

%display(2 digits after the decimal point)

%display(15 digits after the decimal point)

Add a + sign

Decimal point(Default)

Decimal point(2 digits)

Decimal point(0 digits)

Decimal point(12 digits)

Fixed point (default)

Fixed point (2 digits)

Fixed point (no decimal point)

Fixed point (argument is decimal)

Specify a variable in the argument

Variables and strings are in error

Variables and numbers are errors

Cannot be specified by index number

NG without index number specification

datetime.date type

datetime.datetime type

Extract individually(Month and second)