279 lines
9.8 KiB
Python
279 lines
9.8 KiB
Python
# -*- coding: utf-8 -*-
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"""Advanced string formatting for Python >= 2.4.
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An implementation of the advanced string formatting (PEP 3101).
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Author: Florent Xicluna
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"""
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import re
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if hasattr(str, 'partition'):
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def partition(s, sep):
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return s.partition(sep)
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else: # Python 2.4
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def partition(s, sep):
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try:
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left, right = s.split(sep, 1)
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except ValueError:
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return s, '', ''
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return left, sep, right
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_format_str_re = re.compile(
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r'((?<!{)(?:{{)+' # '{{'
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r'|(?:}})+(?!})' # '}}
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r'|{(?:[^{](?:[^{}]+|{[^{}]*})*)?})' # replacement field
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)
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_format_sub_re = re.compile(r'({[^{}]*})') # nested replacement field
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_format_spec_re = re.compile(
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r'((?:[^{}]?[<>=^])?)' # alignment
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r'([-+ ]?)' # sign
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r'(#?)' r'(\d*)' r'(,?)' # base prefix, minimal width, thousands sep
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r'((?:\.\d+)?)' # precision
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r'(.?)$' # type
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)
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_field_part_re = re.compile(
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r'(?:(\[)|\.|^)' # start or '.' or '['
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r'((?(1)[^]]*|[^.[]*))' # part
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r'(?(1)(?:\]|$)([^.[]+)?)' # ']' and invalid tail
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)
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if hasattr(re, '__version__'):
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_format_str_sub = _format_str_re.sub
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else:
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# Python 2.4 fails to preserve the Unicode type
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def _format_str_sub(repl, s):
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if isinstance(s, unicode):
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return unicode(_format_str_re.sub(repl, s))
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return _format_str_re.sub(repl, s)
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if hasattr(int, '__index__'):
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def _is_integer(value):
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return hasattr(value, '__index__')
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else: # Python 2.4
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def _is_integer(value):
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return isinstance(value, (int, long))
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def _strformat(value, format_spec=""):
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"""Internal string formatter.
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It implements the Format Specification Mini-Language.
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"""
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m = _format_spec_re.match(str(format_spec))
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if not m:
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raise ValueError('Invalid conversion specification')
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align, sign, prefix, width, comma, precision, conversion = m.groups()
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is_numeric = hasattr(value, '__float__')
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is_integer = is_numeric and _is_integer(value)
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if prefix and not is_integer:
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raise ValueError('Alternate form (#) not allowed in %s format '
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'specifier' % (is_numeric and 'float' or 'string'))
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if is_numeric and conversion == 'n':
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# Default to 'd' for ints and 'g' for floats
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conversion = is_integer and 'd' or 'g'
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elif sign:
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if not is_numeric:
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raise ValueError("Sign not allowed in string format specifier")
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if conversion == 'c':
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raise ValueError("Sign not allowed with integer "
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"format specifier 'c'")
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if comma:
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# TODO: thousand separator
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pass
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try:
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if ((is_numeric and conversion == 's') or
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(not is_integer and conversion in set('cdoxX'))):
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raise ValueError
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if conversion == 'c':
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conversion = 's'
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value = chr(value % 256)
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rv = ('%' + prefix + precision + (conversion or 's')) % (value,)
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except ValueError:
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raise ValueError("Unknown format code %r for object of type %r" %
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(conversion, value.__class__.__name__))
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if sign not in '-' and value >= 0:
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# sign in (' ', '+')
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rv = sign + rv
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if width:
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zero = (width[0] == '0')
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width = int(width)
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else:
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zero = False
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width = 0
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# Fastpath when alignment is not required
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if width <= len(rv):
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if not is_numeric and (align == '=' or (zero and not align)):
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raise ValueError("'=' alignment not allowed in string format "
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"specifier")
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return rv
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fill, align = align[:-1], align[-1:]
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if not fill:
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fill = zero and '0' or ' '
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if align == '^':
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padding = width - len(rv)
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# tweak the formatting if the padding is odd
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if padding % 2:
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rv += fill
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rv = rv.center(width, fill)
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elif align == '=' or (zero and not align):
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if not is_numeric:
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raise ValueError("'=' alignment not allowed in string format "
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"specifier")
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if value < 0 or sign not in '-':
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rv = rv[0] + rv[1:].rjust(width - 1, fill)
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else:
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rv = rv.rjust(width, fill)
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elif align in ('>', '=') or (is_numeric and not align):
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# numeric value right aligned by default
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rv = rv.rjust(width, fill)
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else:
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rv = rv.ljust(width, fill)
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return rv
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def _format_field(value, parts, conv, spec, want_bytes=False):
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"""Format a replacement field."""
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for k, part, _ in parts:
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if k:
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if part.isdigit():
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value = value[int(part)]
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else:
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value = value[part]
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else:
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value = getattr(value, part)
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if conv:
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value = ((conv == 'r') and '%r' or '%s') % (value,)
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if hasattr(value, '__format__'):
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value = value.__format__(spec)
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elif hasattr(value, 'strftime') and spec:
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value = value.strftime(str(spec))
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else:
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value = _strformat(value, spec)
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if want_bytes and isinstance(value, unicode):
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return str(value)
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return value
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class FormattableString(object):
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"""Class which implements method format().
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The method format() behaves like str.format() in python 2.6+.
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>>> FormattableString(u'{a:5}').format(a=42)
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... # Same as u'{a:5}'.format(a=42)
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u' 42'
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"""
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__slots__ = '_index', '_kwords', '_nested', '_string', 'format_string'
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def __init__(self, format_string):
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self._index = 0
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self._kwords = {}
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self._nested = {}
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self.format_string = format_string
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self._string = _format_str_sub(self._prepare, format_string)
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def __eq__(self, other):
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if isinstance(other, FormattableString):
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return self.format_string == other.format_string
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# Compare equal with the original string.
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return self.format_string == other
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def _prepare(self, match):
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# Called for each replacement field.
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part = match.group(0)
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if part[0] == part[-1]:
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# '{{' or '}}'
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assert part == part[0] * len(part)
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return part[:len(part) // 2]
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repl = part[1:-1]
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field, _, format_spec = partition(repl, ':')
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literal, sep, conversion = partition(field, '!')
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if sep and not conversion:
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raise ValueError("end of format while looking for "
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"conversion specifier")
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if len(conversion) > 1:
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raise ValueError("expected ':' after format specifier")
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if conversion not in 'rsa':
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raise ValueError("Unknown conversion specifier %s" %
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str(conversion))
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name_parts = _field_part_re.findall(literal)
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if literal[:1] in '.[':
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# Auto-numbering
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if self._index is None:
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raise ValueError("cannot switch from manual field "
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"specification to automatic field numbering")
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name = str(self._index)
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self._index += 1
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if not literal:
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del name_parts[0]
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else:
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name = name_parts.pop(0)[1]
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if name.isdigit() and self._index is not None:
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# Manual specification
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if self._index:
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raise ValueError("cannot switch from automatic field "
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"numbering to manual field specification")
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self._index = None
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empty_attribute = False
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for k, v, tail in name_parts:
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if not v:
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empty_attribute = True
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if tail:
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raise ValueError("Only '.' or '[' may follow ']' "
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"in format field specifier")
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if name_parts and k == '[' and not literal[-1] == ']':
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raise ValueError("Missing ']' in format string")
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if empty_attribute:
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raise ValueError("Empty attribute in format string")
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if '{' in format_spec:
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format_spec = _format_sub_re.sub(self._prepare, format_spec)
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rv = (name_parts, conversion, format_spec)
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self._nested.setdefault(name, []).append(rv)
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else:
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rv = (name_parts, conversion, format_spec)
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self._kwords.setdefault(name, []).append(rv)
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return r'%%(%s)s' % id(rv)
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def format(self, *args, **kwargs):
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"""Same as str.format() and unicode.format() in Python 2.6+."""
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if args:
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kwargs.update(dict((str(i), value)
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for (i, value) in enumerate(args)))
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# Encode arguments to ASCII, if format string is bytes
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want_bytes = isinstance(self._string, str)
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params = {}
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for name, items in self._kwords.items():
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value = kwargs[name]
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for item in items:
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parts, conv, spec = item
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params[str(id(item))] = _format_field(value, parts, conv, spec,
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want_bytes)
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for name, items in self._nested.items():
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value = kwargs[name]
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for item in items:
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parts, conv, spec = item
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spec = spec % params
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params[str(id(item))] = _format_field(value, parts, conv, spec,
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want_bytes)
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return self._string % params
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def selftest():
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import datetime
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F = FormattableString
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assert F(u"{0:{width}.{precision}s}").format('hello world',
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width=8, precision=5) == u'hello '
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d = datetime.date(2010, 9, 7)
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assert F(u"The year is {0.year}").format(d) == u"The year is 2010"
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assert F(u"Tested on {0:%Y-%m-%d}").format(d) == u"Tested on 2010-09-07"
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print 'Test successful'
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if __name__ == '__main__':
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selftest()
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