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python string formatting with call to .format()
Field definitionsreplacement_field | "{" [field_name] ["!" conversion] [":" format_spec] "}"
| field_name | arg_name ("." attribute_name | "[" element_index "]")*
| arg_name | [identifier | digit+]
| attribute_name | identifier
| element_index | digit+ | index_string
| index_string | <any source character except "]"> +
| conversion | "r" | "s" | "a"
| format_spec | Format Specification Mini-Language
|
field_nameThe replacement_field can start with a field_name to specify the object whose value is to be formatted and inserted.
The field_name begins with an arg_name. The arg_name can be followed by any number of index or attribute expressions. |
arg_nameAn arg_name is either a number or a keyword. If it's a number it refers to a positional argument. If it's a keyword, it refers to a named keyword argument. If the numerical arg_names in a format string are 0,1,2 in sequence, the can be omitted (They are automatically inserted). |
attribute_nameAn expression of the form '.name' selects the named attribute using getattr() |
element_indexAn expression of the form '[index]' does an index lookup using __getitem__().
For example:
List index: [0]
Dictionary: [name] |
conversion!s | calls str() | !r | calls repr() | !a | calls ascii() |
The conversion field forces a type conversion before formatting, so not by the __format__() method of the value itself. String presentation typess
| String format. This is the default for strings | None | The same as s |
Integer presentation typesb
| Binary format. Outputs the number in base 2 | c
| Character. Converts the integer to unicode | d
| Decimal integer. Outputs number in base 10 | o
| Octal format. Outputs number in base 8 | x
| Hex format. Outputs number in base 16 using lowercase letters | X
| Hex format. Outputs number in base 16 using uppercase letters | n
| Number. Same as d but uses current locale setting for the separator | None | Same as d |
| | Format Specification Mini-Languageformat_spec | [[fill]align][sign][#][0][width][grouping_option][.precision][type]
| fill | <any character>
| align | "<" | ">" | "=" | "^"
| sign | "+" | "-" | " "
| width | digit+
| grouping_option | "_" | ","
| precision | digit+
| type | "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g" | "G" | "n" | "o" | "s" | "x" | "X" | "%"
|
fill, sign and align<
| Force left-alignment within available space | >
| Force rigth-alignment within available space | =
| Only valid for numeric types. Forces the padding to be placed after the sign but before the digits | ^
| Forces the field to be centered within available space | +
| Use a sign for both positiv and negative numbers | -
| Use sign only for negative numbers | space
| Use a leading space for positiv numbers and a minus sign for negative numbers | #
| Causes the alternate form to be used for the conversion. binary: 0b, octal: 0o and hex: 0x. For floats, complex and Decimal types that causes to contain a trailing decimal-point even if no digits follow it | ,
| Use , for thousands separator | _
| Use _ for thousands separator |
If an align value is specified it can be preceded by a fill character, that can be any character (default is space)
The sign option is only valid on numeric types width and precisionwidth is a decimal integer defining the minimum field width. A leading 0 enables sign-aware zero-padding for numeric types.
precision is a decimal number indicating how many digits should be displayed after the decimal point. For non-number types it indicates the maximum field-size. Not allowed for integer values |
Floating point and decimal presentation typese
| Exponent notation using the letter e to indicate the exponent. Default precision is 6 | E
| Exponent notation. Same as e but with uppercase E | f
| Fixed-point notation. Default precision is 6 | F
| Fixed-point notation. Same as f but converts nan to NAN and inf to INF | g
| General format. If precision is p>=1 this rounds the number to p significant digits. Output format is either fixed-point or in scientific notation, depending on the magnitude | G
| General format. Same as g but switches to E if the number gets too large. | n
| Number. Same as g but use current locale for the number separator character | %
| Percentage. Multiplies number by 100 and displays it in f format followed by a percentage sign | None | Same as g but fixed-point notation has at least one digit past the decimal point |
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