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# Copyright 2019 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
import string
def format_template(format_string, *args, **kwargs):
"""
Formats a string like the built-in |format| allowing unbound keys.
format_template("${template_var} {format_var}", format_var=42)
will produce
"${template_var} 42"
without raising an exception that |template_var| is unbound.
"""
return _template_formatter.format(format_string, *args, **kwargs)
class _TemplateFormatter(string.Formatter):
def get_value(self, key, args, kwargs):
if isinstance(key, int):
return args[key]
value = kwargs.get(key)
if value is None:
return "{" + key + "}"
else:
return value
_template_formatter = _TemplateFormatter()
class NonRenderable(object):
"""
Represents a non-renderable object.
Unlike a template variable bound to None, which is a valid Python value,
this object raises an exception when rendered, just like an unbound template
variable.
"""
def __init__(self, error_message="Undefined"):
self._error_message = error_message
def __bool__(self):
raise NameError(self._error_message)
def __str__(self):
raise NameError(self._error_message)
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