gument first
   "Bring out the holy {name!r}"    # Calls repr() on the argument first
   "More {!a}"                      # Calls ascii() on the argument first

The *format_spec* field contains a specification of how the value
should be presented, including such details as field width, alignment,
padding, decimal precision and so on.  Each value type can define its
own “formatting mini-language” or interpretation of the *format_spec*.

Most built-in types support a common formatting mini-language, which
is described in the next section.

A *format_spec* field can also include nested replacement fields
within it. These nested replacement fields may contain a field name,
conversion flag and format specification, but deeper nesting is not
allowed.  The replacement fields within the format_spec are
substituted before the *format_spec* string is interpreted. This
allows the formatting of a value to be dynamically specified.

See the Format examples section for some examples.


Format Specification Mini-Language
==================================

“Format specifications” are used within replacement fields contained
within a format string to define how individual values are presented
(see Format String Syntax and f-strings). They can also be passed
directly to the built-in "format()" function.  Each formattable type
may define how the format specification is to be interpreted.

Most built-in types implement the following options for format
specifications, although some of the formatting options are only
supported by the numeric types.

A general convention is that an empty format specification produces
the same result as if you had called "str()" on the value. A non-empty
format specification typically modifies the result.

The general form of a *standard format specifier* is:

   format_spec ::= [options][width][grouping]["." precision][type]
   options     ::= [[fill]align][sign]["z"]["#"]["0"]
   fill        ::= <any character>
   align       ::= "<" | ">" | "=" | "^"
   sign        ::= "+" | "-" | " "
   width       ::= digit+
   grouping    ::= "," | "_"
   precision   ::= digit+
   type        ::= "b" | "c" | "d" | "e" | "E" | "f" | "F" | "g"
                   | "G" | "n" | "o" | "s" | "x" | "X" | "%"

If a valid *align* value is specified, it can be preceded by a *fill*
character that can be any character and defaults to a space if
omitted. It is not possible to use a literal curly brace (”"{"” or
“"}"”) as the *fill* character in a formatted string literal or when
using the "str.format()" method.  However, it is possible to insert a
curly brace with a nested replacement field.  This limitation doesn’t
affect the "format()" function.

The meaning of the various alignment options is as follows:

+-----------+------------------------------------------------------------+
| Option    | Meaning                                                    |
|===========|============================================================|
| "'<'"     | Forces the field to be left-aligned within the available   |
|           | space (this is the default for most objects).              |
+-----------+------------------------------------------------------------+
| "'>'"     | Forces the field to be right-aligned within the available  |
|           | space (this is the default for numbers).                   |
+-----------+------------------------------------------------------------+
| "'='"     | Forces the padding to be placed after the sign (if any)    |
|           | but before the digits.  This is used for printing fields   |
|           | in the form ‘+000000120’. This alignment option is only    |
|           | valid for numeric types, excluding "complex". It becomes   |
|           | the default for numbers when ‘0’ immediately precedes the  |
|           | field width.                                               |
+-----------+------------------------------------------------------------+
| "'^'"     | Forces the field to be centered within the available       |
|           | space.                                                     |
+-----------+------------------------------------------------------------+

Note that unless a minimum field width is defined, the field width
will always be the same size as the data to fill it, so that the
alignment option has no meaning in this case.

The *sign* option is only valid for number types, and can be one of
the following:

+-----------+------------------------------------------------------------+
| Option    | Meaning                                                    |
|===========|============================================================|
| "'+'"     | Indicates that a sign should be used for both positive as  |
|           | well as negative numbers.                                  |
+-----------+------------------------------------------------------------+
| "'-'"     | Indicates that a sign should be used only for negative     |
|           | numbers (this is the default behavior).                    |
+-----------+------------------------------------------------------------+
| space     | Indicates that a leading space should be used on positive  |
|           | numbers, and a minus sign on negative numbers.             |
+-----------+------------------------------------------------------------+

The "'z'" option coerces negative zero floating-point values to
positive zero after rounding to the format precision.  This option is
only valid for floating-point presentation types.

Changed in version 3.11: Added the "'z'" option (see also **PEP
682**).

The "'#'" option causes the “alternate form” to be used for the
conversion.  The alternate form is defined differently for different
types.  This option is only valid for integer, float and complex
types. For integers, when binary, octal, or hexadecimal output is
used, this option adds the respective prefix "'0b'", "'0o'", "'0x'",
or "'0X'" to the output value. For float and complex the alternate
form causes the result of the conversion to always contain a decimal-
point character, even if no digits follow it. Normally, a decimal-
point character appears in the result of these conversions only if a
digit follows it. In addition, for "'g'" and "'G'" conversions,
trailing zeros are not removed from the result.

The *width* is a decimal integer defining the minimum total field
width, including any prefixes, separators, and other formatting
characters. If not specified, then the field width will be determined
by the content.

When no explicit alignment is given, preceding the *width* field by a
zero ("'0'") character enables sign-aware zero-padding for numeric
types, excluding "complex".  This is equivalent to a *fill* character
of "'0'" with an *alignment* type of "'='".

Changed in version 3.10: Preceding the *width* field by "'0'" no
longer affects the default alignment for strings.

The *grouping* option after the *width* field specifies a digit group
separator for the integral part of a number. It can be one of the
following:

+-----------+------------------------------------------------------------+
| Option    | Meaning                                                    |
|===========|============================================================|
| "','"     | Inserts a comma every 3 digits for integer presentation    |
|           | type "'d'" and floating-point presentation types,          |
|           | excluding "'n'". For other presentation types, this option |
|           | is not supported.                                          |
+-----------+------------------------------------------------------------+
| "'_'"     | Inserts an underscore every 3 digits for integer           |
|           | presentation type "'d'" and floating-point presentation    |
|           | types, excluding "'n'". For integer presentation types     |
|           | "'b'", "'o'", "'x'", and "'X'", underscores are inserted   |
|           | every 4 digits. For other presentation types, this option  |
|           | is not supported.                                          |
+-----------+------------------------------------------------------------+

For a locale aware separator, use the "'n'" presentation type instead.

Changed in version 3.1: Added the "','" option (see also **PEP 378**).

Changed in version 3.6: Added the "'_'" option (see also **PEP 515**).

The *precision* is a decimal integer indicating how many digits should
be displayed after the decimal point for presentation types "'f'" and
"'F'", or before and after the decimal point for presentation types
"'g'" or "'G'".  For string presentation types the field indicates the
maximum field size - in other words, how many characters will be used
from the field content.  The *precision* is not allowed for integer
presentation types.

Finally, the *type* determines how the data should be presented.

The available string presentation types are:

   +-----------+------------------------------------------------------------+
   | Type      | Meaning                                                    |
   |===========|============================================================|
   | "'s'"     | String format. This is the default type for strings and    |
   |           | may be omitted.                                            |
   +-----------+------------------------------------------------------------+
   | None      | The same as "'s'".                                         |
   +-----------+------------------------------------------------------------+

The available integer presentation types are:

   +-----------+------------------------------------------------------------+
   | Type      | Meaning                                                    |
   |===========|============================================================|
   | "'b'"     | Binary format. Outputs the number in base 2.               |
   +-----------+------------------------------------------------------------+
   | "'c'"     | Character. Converts the integer to the corresponding       |
   |           | unicode character before printing.                         |
   +-----------+------------------------------------------------------------+
   | "'d'"     | Decimal Integer. Outputs the number in base 10.            |
   +-----------+------------------------------------------------------------+
   | "'o'"     | Octal format. Outputs the number in base 8.                |
   +-----------+------------------------------------------------------------+
   | "'x'"     | Hex format. Outputs the number in base 16, using lower-    |
   |           | case letters for the digits above 9.                       |
   +-----------+------------------------------------------------------------+
   | "'X'"     | Hex format. Outputs the number in base 16, using upper-    |
   |           | case letters for the digits above 9. In case "'#'" is      |
   |           | specified, the prefix "'0x'" will be upper-cased to "'0X'" |
   |           | as well.                                                   |
   +-----------+------------------------------------------------------------+
   | "'n'"     | Number. This is the same as "'d'", except that it uses the |
   |           | current locale setting to insert the appropriate digit     |
   |           | group separators.                                          |
   +-----------+------------------------------------------------------------+
   | None      | The same as "'d'".                                         |
   +-----------+------------------------------------------------------------+

In addition to the above presentation types, integers can be formatted
with the floating-point presentation types listed below (except "'n'"
and "None"). When doing so, "float()" is used to convert the integer
to a floating-point number before formatting.

The available presentation types for "float" and "Decimal" values are:

   +-----------+------------------------------------------------------------+
   | Type      | Meaning                                                    |
   |===========|============================================================|
   | "'e'"     | Scientific notation. For a given precision "p", formats    |
   |           | the number in scientific notation with the letter ‘e’      |
   |           | separating the coefficient from the exponent. The          |
   |           | coefficient has one digit before and "p" digits after the  |
   |           | decimal point, for a total of "p + 1" significant digits.  |
   |           | With no precision given, uses a precision of "6" digits    |
   |           | after the decimal point for "float", and shows all         |
   |           | coefficient digits for "Decimal".  If "p=0", the decimal   |
   |           | point is omitted unless the "#" option is used.            |
   +-----------+------------------------------------------------------------+
   | "'E'"     | Scientific notation. Same as "'e'" except it uses an upper |
   |           | case ‘E’ as the separator character.                       |
   +-----------+------------------------------------------------------------+
   | "'f'"     | Fixed-point notation. For a given precision "p", formats   |
   |           | the number as a decimal number with exactly "p" digits     |
   |           | following the decimal point. With no precision given, uses |
   |           | a precision of "6" digits after the decimal point for      |
   |           | "float", and uses a precision large enough to show all     |
   |           | coefficient digits for "Decimal".  If "p=0", the decimal   |
   |           | point is omitted unless the "#" option is used.            |
   +-----------+------------------------------------------------------------+
   | "'F'"     | Fixed-point notation. Same as "'f'", but converts "nan" to |
   |           | "NAN" and "inf" to "INF".                                  |
   +-----------+------------------------------------------------------------+
   | "'g'"     | General format.  For a given precision "p >= 1", this      |
   |           | rounds the number to "p" significant digits and then       |
   |           | formats the result in either fixed-point format or in      |
   |           | scientific notation, depending on its magnitude. A         |
   |           | precision of "0" is treated as equivalent to a precision   |
   |           | of "1".  The precise rules are as follows: suppose that    |
   |           | the result formatted with presentation type "'e'" and      |
   |           | precision "p-1" would have exponent "exp".  Then, if "m <= |
   |           | exp < p", where "m" is -4 for floats and -6 for            |
   |           | "Decimals", the number is formatted with presentation type |
   |           | "'f'" and precision "p-1-exp".  Otherwise, the number is   |
   |           | formatted with presentation type "'e'" and precision       |
   |           | "p-1". In both cases insignificant trailing zeros are      |
   |           | removed from the significand, and the decimal point is     |
   |           | also removed if there are no remaining digits following    |
   |           | it, unless the "'#'" option is used.  With no precision    |
   |           | given, uses a precision of "6" significant digits for      |
   |           | "float". For "Decimal", the coefficient of the result is   |
   |           | formed from the coefficient digits of the value;           |
   |           | scientific notation is used for values smaller than "1e-6" |
   |           | in absolute value and values where the place value of the  |
   |           | least significant digit is larger than 1, and fixed-point  |
   |           | notation is used otherwise.  Positive and negative         |
   |           | infinity, positive and negative zero, and nans, are        |
   |           | formatted as "inf", "-inf", "0", "-0" and "nan"            |
   |           | respectively, regardless of the precision.                 |
   +-----------+------------------------------------------------------------+
   | "'G'"     | General format. Same as "'g'" except switches to "'E'" if  |
   |           | the number gets too large. The representations of infinity |
   |           | and NaN are uppercased, too.                               |
   +-----------+------------------------------------------------------------+
   | "'n'"     | Number. This is the same as "'g'", except that it uses the |
   |           | current locale setting to insert the appropriate digit     |
   |           | group separators for the integral part of a number.        |
   +-----------+------------------------------------------------------------+
   | "'%'"     | Percentage. Multiplies the number by 100 and displays in   |
   |           | fixed ("'f'") format, followed by a percent sign.          |
   +-----------+------------------------------------------------------------+
   | None      | For "float" this is like the "'g'" type, except that when  |
   |           | fixed- point notation is used to format the result, it     |
   |           | always includes at least one digit past the decimal point, |
   |           | and switches to the scientific notation when "exp >= p -   |
   |           | 1".  When the precision is not specified, the latter will  |
   |           | be as large as needed to represent the given value         |
   |           | faithfully.  For "Decimal", this is the same as either     |
   |           | "'g'" or "'G'" depending on the value of                   |
   |           | "context.capitals" for the current decimal context.  The   |
   |           | overall effect is to match the output of "str()" as        |
   |           | altered by the other format modifiers.                     |
   +-----------+------------------------------------------------------------+

The result should be correctly rounded to a given precision "p" of
digits after the decimal point.  The rounding mode for "float" matches
that of the "round()" builtin.  For "Decimal", the rounding mode of
the current context will be used.

The available presentation types for "complex" are the same as those
for "float" ("'%'" is not allowed).  Both the real and imaginary
components of a complex number are formatted as floating-point
numbers, according to the specified presentation type.  They are
separated by the mandatory sign of the imaginary part, the latter
being terminated by a "j" suffix.  If the presentation type is
missing, the result will match the output of "str()" (complex numbers
with a non-zero real part are also surrounded by parentheses),
possibly altered by other format modifiers.


Format examples
===============

This section contains examples of the "str.format()" syntax and
comparison with the old "%"-formatting.

In most of the cases the syntax is similar to the old "%"-formatting,
with the addition of the "{}" and with ":" used instead of "%". For
example, "'%03.2f'" can be translated to "'{:03.2f}'".

The new format syntax also supports new and different options, shown
in the following examples.

Accessing arguments by position:

   >>> '{0}, {1}, {2}'.format('a', 'b', 'c')
   'a, b, c'
   >>> '{}, {}, {}'.format('a', 'b', 'c')  # 3.1+ only
   'a, b, c'
   >>> '{2}, {1}, {0}'.format('a', 'b', 'c')
   'c, b, a'
   >>> '{2}, {1}, {0}'.format(*'abc')      # unpacking argument sequence
   'c, b, a'
   >>> '{0}{1}{0}'.format('abra', 'cad')   # arguments' indices can be repeated
   'abracadabra'

Accessing arguments by name:

   >>> 'Coordinates: {latitude}, {longitude}'.format(latitude='37.24N', longitude='-115.81W')
   'Coordinates: 37.24N, -115.81W'
   >>> coord = {'latitude': '37.24N', 'longitude': '-115.81W'}
   >>> 'Coordinates: {latitude}, {longitude}'.format(**coord)
   'Coordinates: 37.24N, -115.81W'

Accessing arguments’ attributes:

   >>> c = 3-5j
   >>> ('The complex number {0} is formed from the real part {0.real} '
   ...  'and the imaginary part {0.imag}.').format(c)
   'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0.'
   >>> class Point:
   ...     def __init__(self, x, y):
   ...         self.x, self.y = x, y
   ...     def __str__(self):
   ...         return 'Point({self.x}, {self.y})'.format(self=self)
   ...
   >>> str(Point(4, 2))
   'Point(4, 2)'

Accessing arguments’ items:

   >>> coord = (3, 5)
   >>> 'X: {0[0]};  Y: {0[1]}'.format(coord)
   'X: 3;  Y: 5'

Replacing "%s" and "%r":

   >>> "repr() shows quotes: {!r}; str() doesn't: {!s}".format('test1', 'test2')
   "repr() shows quotes: 'test1'; str() doesn't: test2"

Aligning the text and specifying a width:

   >>> '{:<30}'.format('left aligned')
   'left aligned                  '
   >>> '{:>30}'.format('right aligned')
   '                 right aligned'
   >>> '{:^30}'.format('centered')
   '           centered           '
   >>> '{:*^30}'.format('centered')  # use '*' as a fill char
   '***********centered***********'

Replacing "%+f", "%-f", and "% f" and specifying a sign:

   >>> '{:+f}; {:+f}'.format(3.14, -3.14)  # show it always
   '+3.140000; -3.140000'
   >>> '{: f}; {: f}'.format(3.14, -3.14)  # show a space for positive numbers
   ' 3.140000; -3.140000'
   >>> '{:-f}; {:-f}'.format(3.14, -3.14)  # show only the minus -- same as '{:f}; {:f}'
   '3.140000; -3.140000'

Replacing "%x" and "%o" and converting the value to different bases:

   >>> # format also supports binary numbers
   >>> "int: {0:d};  hex: {0:x};  oct: {0:o};  bin: {0:b}".format(42)
   'int: 42;  hex: 2a;  oct: 52;  bin: 101010'
   >>> # with 0x, 0o, or 0b as prefix:
   >>> "int: {0:d};  hex: {0:#x};  oct: {0:#o};  bin: {0:#b}".format(42)
   'int: 42;  hex: 0x2a;  oct: 0o52;  bin: 0b101010'

Using the comma or the underscore as a digit group separator:

   >>> '{:,}'.format(1234567890)
   '1,234,567,890'
   >>> '{:_}'.format(1234567890)
   '1_234_567_890'
   >>> '{:_b}'.format(1234567890)
   '100_1001_1001_0110_0000_0010_1101_0010'
   >>> '{:_x}'.format(1234567890)
   '4996_02d2'

Expressing a percentage:

   >>> points = 19
   >>> total = 22
   >>> 'Correct answers: {:.2%}'.format(points/total)
   'Correct answers: 86.36%'

Using type-specific formatting:

   >>> import datetime
   >>> d = datetime.datetime(2010, 7, 4, 12, 15, 58)
   >>> '{:%Y-%m-%d %H:%M:%S}'.format(d)
   '2010-07-04 12:15:58'

Nesting arguments and more complex examples:

   >>> for align, text in zip('<^>', ['left', 'center', 'right']):
   ...     '{0:{fill}{align}16}'.format(text, fill=align, align=align)
   ...
   'left<<<<<<<<<<<<'
   '^^^^^center^^^^^'
   '>>>>>>>>>>>right'
   >>>
   >>> octets = [192, 168, 0, 1]
   >>> '{:02X}{:02X}{:02X}{:02X}'.format(*octets)
   'C0A80001'
   >>> int(_, 16)
   3232235521
   >>>
   >>> width = 5
   >>> for num in range(5,12):
   ...     for base in 'dXob':
   ...         print('{0:{width}{base}}'.format(num, base=base, width=width), end=' ')
   ...     print()
   ...
       5     5     5   101
       6     6     6   110
       7     7     7   111
       8     8    10  1000
       9     9    11  1001
      10     A    12  1010
      11     B    13  1011
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