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annotate planemo/lib/python3.7/site-packages/boltons/formatutils.py @ 1:56ad4e20f292 draft

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"planemo upload commit 6eee67778febed82ddd413c3ca40b3183a3898f1"
author guerler
date Fri, 31 Jul 2020 00:32:28 -0400
parents d30785e31577
children
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1 # -*- coding: utf-8 -*-
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2 """`PEP 3101`_ introduced the :meth:`str.format` method, and what
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3 would later be called "new-style" string formatting. For the sake of
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4 explicit correctness, it is probably best to refer to Python's dual
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5 string formatting capabilities as *bracket-style* and
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6 *percent-style*. There is overlap, but one does not replace the
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7 other.
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8
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9 * Bracket-style is more pluggable, slower, and uses a method.
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10 * Percent-style is simpler, faster, and uses an operator.
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11
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12 Bracket-style formatting brought with it a much more powerful toolbox,
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13 but it was far from a full one. :meth:`str.format` uses `more powerful
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14 syntax`_, but `the tools and idioms`_ for working with
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15 that syntax are not well-developed nor well-advertised.
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16
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17 ``formatutils`` adds several functions for working with bracket-style
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18 format strings:
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19
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20 * :class:`DeferredValue`: Defer fetching or calculating a value
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21 until format time.
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22 * :func:`get_format_args`: Parse the positional and keyword
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23 arguments out of a format string.
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24 * :func:`tokenize_format_str`: Tokenize a format string into
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25 literals and :class:`BaseFormatField` objects.
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26 * :func:`construct_format_field_str`: Assists in progammatic
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27 construction of format strings.
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28 * :func:`infer_positional_format_args`: Converts anonymous
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29 references in 2.7+ format strings to explicit positional arguments
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30 suitable for usage with Python 2.6.
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31
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32 .. _more powerful syntax: https://docs.python.org/2/library/string.html#format-string-syntax
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33 .. _the tools and idioms: https://docs.python.org/2/library/string.html#string-formatting
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34 .. _PEP 3101: https://www.python.org/dev/peps/pep-3101/
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35 """
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36 # TODO: also include percent-formatting utils?
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37 # TODO: include lithoxyl.formatters.Formatter (or some adaptation)?
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38
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39 from __future__ import print_function
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40
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41 import re
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42 from string import Formatter
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43
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44 try:
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45 unicode # Python 2
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46 except NameError:
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47 unicode = str # Python 3
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48
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49 __all__ = ['DeferredValue', 'get_format_args', 'tokenize_format_str',
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50 'construct_format_field_str', 'infer_positional_format_args',
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51 'BaseFormatField']
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52
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53
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54 _pos_farg_re = re.compile('({{)|' # escaped open-brace
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55 '(}})|' # escaped close-brace
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56 r'({[:!.\[}])') # anon positional format arg
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57
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58
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59 def construct_format_field_str(fname, fspec, conv):
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60 """
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61 Constructs a format field string from the field name, spec, and
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62 conversion character (``fname``, ``fspec``, ``conv``). See Python
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63 String Formatting for more info.
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64 """
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65 if fname is None:
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66 return ''
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67 ret = '{' + fname
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68 if conv:
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69 ret += '!' + conv
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70 if fspec:
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71 ret += ':' + fspec
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72 ret += '}'
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73 return ret
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74
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75
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76 def split_format_str(fstr):
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77 """Does very basic splitting of a format string, returns a list of
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78 strings. For full tokenization, see :func:`tokenize_format_str`.
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79
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80 """
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81 ret = []
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82
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83 for lit, fname, fspec, conv in Formatter().parse(fstr):
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84 if fname is None:
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85 ret.append((lit, None))
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86 continue
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87 field_str = construct_format_field_str(fname, fspec, conv)
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88 ret.append((lit, field_str))
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89 return ret
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90
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91
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92 def infer_positional_format_args(fstr):
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93 """Takes format strings with anonymous positional arguments, (e.g.,
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94 "{}" and {:d}), and converts them into numbered ones for explicitness and
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95 compatibility with 2.6.
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96
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97 Returns a string with the inferred positional arguments.
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98 """
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99 # TODO: memoize
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100 ret, max_anon = '', 0
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101 # look for {: or {! or {. or {[ or {}
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102 start, end, prev_end = 0, 0, 0
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103 for match in _pos_farg_re.finditer(fstr):
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104 start, end, group = match.start(), match.end(), match.group()
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105 if prev_end < start:
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106 ret += fstr[prev_end:start]
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107 prev_end = end
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108 if group == '{{' or group == '}}':
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109 ret += group
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110 continue
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111 ret += '{%s%s' % (max_anon, group[1:])
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112 max_anon += 1
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113 ret += fstr[prev_end:]
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114 return ret
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115
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116
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117 # This approach is hardly exhaustive but it works for most builtins
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118 _INTCHARS = 'bcdoxXn'
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119 _FLOATCHARS = 'eEfFgGn%'
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120 _TYPE_MAP = dict([(x, int) for x in _INTCHARS] +
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121 [(x, float) for x in _FLOATCHARS])
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122 _TYPE_MAP['s'] = str
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123
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124
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125 def get_format_args(fstr):
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126 """
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127 Turn a format string into two lists of arguments referenced by the
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128 format string. One is positional arguments, and the other is named
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129 arguments. Each element of the list includes the name and the
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130 nominal type of the field.
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131
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132 # >>> get_format_args("{noun} is {1:d} years old{punct}")
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133 # ([(1, <type 'int'>)], [('noun', <type 'str'>), ('punct', <type 'str'>)])
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134
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135 # XXX: Py3k
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136 >>> get_format_args("{noun} is {1:d} years old{punct}") == \
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137 ([(1, int)], [('noun', str), ('punct', str)])
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138 True
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139 """
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140 # TODO: memoize
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141 formatter = Formatter()
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142 fargs, fkwargs, _dedup = [], [], set()
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143
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144 def _add_arg(argname, type_char='s'):
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145 if argname not in _dedup:
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146 _dedup.add(argname)
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147 argtype = _TYPE_MAP.get(type_char, str) # TODO: unicode
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148 try:
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149 fargs.append((int(argname), argtype))
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150 except ValueError:
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151 fkwargs.append((argname, argtype))
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152
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153 for lit, fname, fspec, conv in formatter.parse(fstr):
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154 if fname is not None:
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155 type_char = fspec[-1:]
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156 fname_list = re.split('[.[]', fname)
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157 if len(fname_list) > 1:
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158 raise ValueError('encountered compound format arg: %r' % fname)
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159 try:
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160 base_fname = fname_list[0]
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161 assert base_fname
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162 except (IndexError, AssertionError):
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163 raise ValueError('encountered anonymous positional argument')
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164 _add_arg(fname, type_char)
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165 for sublit, subfname, _, _ in formatter.parse(fspec):
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166 # TODO: positional and anon args not allowed here.
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167 if subfname is not None:
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168 _add_arg(subfname)
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169 return fargs, fkwargs
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170
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171
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172 def tokenize_format_str(fstr, resolve_pos=True):
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173 """Takes a format string, turns it into a list of alternating string
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174 literals and :class:`BaseFormatField` tokens. By default, also
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175 infers anonymous positional references into explicit, numbered
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176 positional references. To disable this behavior set *resolve_pos*
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177 to ``False``.
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178 """
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179 ret = []
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180 if resolve_pos:
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181 fstr = infer_positional_format_args(fstr)
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182 formatter = Formatter()
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183 for lit, fname, fspec, conv in formatter.parse(fstr):
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184 if lit:
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185 ret.append(lit)
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186 if fname is None:
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187 continue
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188 ret.append(BaseFormatField(fname, fspec, conv))
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189 return ret
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190
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191
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192 class BaseFormatField(object):
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193 """A class representing a reference to an argument inside of a
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194 bracket-style format string. For instance, in ``"{greeting},
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195 world!"``, there is a field named "greeting".
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196
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197 These fields can have many options applied to them. See the
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198 Python docs on `Format String Syntax`_ for the full details.
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199
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200 .. _Format String Syntax: https://docs.python.org/2/library/string.html#string-formatting
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201 """
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202 def __init__(self, fname, fspec='', conv=None):
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203 self.set_fname(fname)
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204 self.set_fspec(fspec)
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205 self.set_conv(conv)
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206
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207 def set_fname(self, fname):
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208 "Set the field name."
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209
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210 path_list = re.split('[.[]', fname) # TODO
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211
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212 self.base_name = path_list[0]
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213 self.fname = fname
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214 self.subpath = path_list[1:]
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215 self.is_positional = not self.base_name or self.base_name.isdigit()
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216
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217 def set_fspec(self, fspec):
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218 "Set the field spec."
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219 fspec = fspec or ''
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220 subfields = []
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221 for sublit, subfname, _, _ in Formatter().parse(fspec):
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222 if subfname is not None:
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223 subfields.append(subfname)
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224 self.subfields = subfields
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225 self.fspec = fspec
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226 self.type_char = fspec[-1:]
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227 self.type_func = _TYPE_MAP.get(self.type_char, str)
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228
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229 def set_conv(self, conv):
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230 """There are only two built-in converters: ``s`` and ``r``. They are
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231 somewhat rare and appearlike ``"{ref!r}"``."""
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232 # TODO
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233 self.conv = conv
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234 self.conv_func = None # TODO
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235
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236 @property
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237 def fstr(self):
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238 "The current state of the field in string format."
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239 return construct_format_field_str(self.fname, self.fspec, self.conv)
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240
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241 def __repr__(self):
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242 cn = self.__class__.__name__
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243 args = [self.fname]
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244 if self.conv is not None:
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245 args.extend([self.fspec, self.conv])
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246 elif self.fspec != '':
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247 args.append(self.fspec)
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248 args_repr = ', '.join([repr(a) for a in args])
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249 return '%s(%s)' % (cn, args_repr)
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250
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251 def __str__(self):
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252 return self.fstr
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253
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254
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255 _UNSET = object()
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256
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257
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258 class DeferredValue(object):
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259 """:class:`DeferredValue` is a wrapper type, used to defer computing
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260 values which would otherwise be expensive to stringify and
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261 format. This is most valuable in areas like logging, where one
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262 would not want to waste time formatting a value for a log message
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263 which will subsequently be filtered because the message's log
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264 level was DEBUG and the logger was set to only emit CRITICAL
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265 messages.
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266
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267 The :class:``DeferredValue`` is initialized with a callable that
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268 takes no arguments and returns the value, which can be of any
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269 type. By default DeferredValue only calls that callable once, and
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270 future references will get a cached value. This behavior can be
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271 disabled by setting *cache_value* to ``False``.
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272
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273 Args:
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274
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275 func (function): A callable that takes no arguments and
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276 computes the value being represented.
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277 cache_value (bool): Whether subsequent usages will call *func*
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278 again. Defaults to ``True``.
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279
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280 >>> import sys
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281 >>> dv = DeferredValue(lambda: len(sys._current_frames()))
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282 >>> output = "works great in all {0} threads!".format(dv)
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283
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284 PROTIP: To keep lines shorter, use: ``from formatutils import
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285 DeferredValue as DV``
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286 """
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287 def __init__(self, func, cache_value=True):
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288 self.func = func
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289 self.cache_value = True
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290 self._value = _UNSET
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291
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292 def get_value(self):
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293 """Computes, optionally caches, and returns the value of the
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294 *func*. If ``get_value()`` has been called before, a cached
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295 value may be returned depending on the *cache_value* option
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296 passed to the constructor.
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297 """
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298 if self._value is not _UNSET and self.cache_value:
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299 value = self._value
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300 else:
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301 value = self.func()
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302 if self.cache_value:
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303 self._value = value
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304 return value
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305
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306 def __int__(self):
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307 return int(self.get_value())
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308
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309 def __float__(self):
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310 return float(self.get_value())
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311
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312 def __str__(self):
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313 return str(self.get_value())
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314
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315 def __unicode__(self):
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316 return unicode(self.get_value())
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317
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318 def __repr__(self):
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319 return repr(self.get_value())
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320
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321 def __format__(self, fmt):
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322 value = self.get_value()
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323
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324 pt = fmt[-1:] # presentation type
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325 type_conv = _TYPE_MAP.get(pt, str)
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326
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327 try:
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328 return value.__format__(fmt)
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329 except (ValueError, TypeError):
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330 # TODO: this may be overkill
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331 return type_conv(value).__format__(fmt)
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332
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333 # end formatutils.py