String Format Specification

Alignment

Default

>>> s = 'aaa'
>>> n = 12

# default
#   - string left aligned
#   - number right aligned
#   - space filled
>>> f'{s:5}'
'aaa  '
>>> f'{n:5}'
'   12'

Direction: <, >, ^

>>> s = 'aaa'
>>> n = 12

# < | left aligned
# > | right aligned
# ^ | centered
>>> f'{s:<5}'
'aaa  '
>>> f'{s:>5}'
'  aaa'
>>> f'{s:^5}'
' AAA '
>>> f'{s:^6}'
' AAA  '

Filled Chars

>>> s = 'aaa'
>>> n = 12

>>> f'{s:#<5}'
'aaa##'

Sign

NOTE: Only for numeric types.

>>> s = 'aaa'
>>> f'{s:f=6}'
ValueError: '=' alignment not allowed in string format specifier

>>> i = 6
>>> j = -2

# -
# the default behavior.
>>> f'{i:0=-5}, {j:0=-5}'
'00006, -0002'
>>> f'{i:0=5}, {j:0=5}'
'00006, -0002'

# +
>>> f'{i:0=+5}, {j:0=+5}'
'+0006, -0002'

# (space)
>>> f'{i:0= 5}, {j:0= 5}'
' 0006, -0002'

Integer

>>> i = 666666
>>> f'{i:d}, {i:n}, {i:b}, {i:o}, {i:x}, {i:X}'
'666666, 666666, 10100010110000101010, 2426052, a2c2a, A2C2A'

Prefix: #

>>> i = 666666
>>> f'{i:#d}, {i:#n}, {i:#b}, {i:#o}, {i:#x}, {i:#X}'
'666666, 666666, 0b10100010110000101010, 0o2426052, 0xa2c2a, 0XA2C2A'

Thousand Seperator: , / _

>>> i = 666666

# , for decimal
>>> f'{i:#,d}'
'666,666'

# _ for binary, octal, hex
>>> f'{i:#_b}, {i:#_o}, {i:#_x}, {i:#_X}'
'0b1010_0010_1100_0010_1010, 0o242_6052, 0xa_2c2a, 0XA_2C2A'

Float

>>> i = 666666.666
>>> f'{i:f}'
'666666.666000'

Thousand Seperator: ,

>>> i = 666666.666
>>> f'{i:,f}, {i:_f}'
'666,666.666000, 666_666.666000'

Field Width and Precision

>>> i = 666666.666

>>> f'{i:f}'  # precision is 6 by default
'666666.666000'

>>> f'{i:.2f}'  # precision is 2
'666666.67'

>>> f'{i:10.2f}'  # width is 10 (space by default), precision is 2
' 666666.67'

>>> f'{i:010.2f}'  # width is 10 (padding with 0), precision is 2
'0666666.67'

Combination examples:

>>> i = 1234.5678
>>> f'{i = :<+10.2f}'  # left-align, width 10, show +, precision 2
'i = +1234.57  '

Date and Time Format

>>> from datetime import datetime
>>> today = datetime(year=2019, month=10, day=24)

>>> f'{today:%B %d, %Y}'  # using date format specifier
'October 24, 2019'
>>> f'{today:%Y-%m-%d %H:%M:%S}'  # using datetime format specifier
'2019-10-24 00:00:00'

References