The f
means Formatted string literals and it’s new in Python 3.6
.
A formatted string literal or f-string is a string literal that is
prefixed with'f'
or'F'
. These strings may contain replacement
fields, which are expressions delimited by curly braces{}
. While
other string literals always have a constant value, formatted strings
are really expressions evaluated at run time.
Some examples of formatted string literals:
>>> name = "Fred"
>>> f"He said his name is {name}."
"He said his name is Fred."
>>> name = "Fred"
>>> f"He said his name is {name!r}."
"He said his name is Fred."
>>> f"He said his name is {repr(name)}." # repr() is equivalent to !r
"He said his name is Fred."
>>> width = 10
>>> precision = 4
>>> value = decimal.Decimal("12.34567")
>>> f"result: {value:{width}.{precision}}" # nested fields
result: 12.35
>>> today = datetime(year=2017, month=1, day=27)
>>> f"{today:%B %d, %Y}" # using date format specifier
January 27, 2017
>>> number = 1024
>>> f"{number:#0x}" # using integer format specifier
0x400