"""
Overview:
Useful utilities for template a string.
"""
from string import Template
from typing import Optional, Mapping, Any
from ..design import SingletonMark
__all__ = [
'env_template'
]
_NO_DEFAULT_VALUE = SingletonMark('_NO_DEFAULT_VALUE')
[docs]def env_template(template: str, environ: Optional[Mapping[str, Any]] = None,
safe: bool = False, default: Any = _NO_DEFAULT_VALUE) -> str:
"""
Overview:
Mapping all the environment values (not system environment variables) into a template string.
Arguments:
- template (:obj:`str`): Template string.
- environ (:obj:`Optional[Mapping[str, str]]`): Environment values, should be a mapping.
- safe (:obj:`bool`): Safe substitute, default is ``False`` which means \
all the value used in template should be able to found in the given ``environ``.
- default (:obj:`Any`): Default value when no variable provided. Default is ``_NO_DEFAULT_VALUE``, which \
means ``KeyError`` will be raised.
Returns:
- result (:obj:`str`): Substituted string.
Examples::
>>> from hbutils.string import env_template
>>> env_template('${A} + 1 = ${B}', {'A': '1', 'B': '2'})
'1 + 1 = 2'
>>> env_template('${A} + 1 = ${B}', {'A': '1'})
KeyError: 'B'
>>> env_template('${A} + 1 = ${B}', {'A': '1'}, safe=True)
'1 + 1 = ${B}'
>>> env_template('${A} + 1 = ${B}', {'A': '1'}, default='') # like environment variable
'1 + 1 = '
"""
class _DefaultDict(dict):
def __getitem__(self, item):
return dict.get(self, item, default)
_template = Template(template)
env = environ or {}
if default is not _NO_DEFAULT_VALUE:
env = _DefaultDict(env)
_func = _template.safe_substitute if safe else _template.substitute
# noinspection PyArgumentList
return _func(env)