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98 lines
3.6 KiB
Python
98 lines
3.6 KiB
Python
"""
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String Utilities:
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This module helps in converting strings from one type to another.
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Currently we have strings of 3 semantic types:
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1. text strings: These strings are used to represent all textual data,
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like people's names, stream names, content of messages, etc.
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These strings can contain non-ASCII characters, so its type should be
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typing.Text (which is `str` in python 3 and `unicode` in python 2).
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2. binary strings: These strings are used to represent binary data.
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This should be of type six.binary_type (which is `bytes` in python 3
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and `str` in python 2).
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3. native strings: These strings are for internal use only. Strings of
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this type are not meant to be stored in database, displayed to end
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users, etc. Things like exception names, parameter names, attribute
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names, etc should be native strings. These strings should only
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contain ASCII characters and they should have type `str`.
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There are 3 utility functions provided for converting strings from one type
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to another - force_text, force_bytes, force_str
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Interconversion between text strings and binary strings can be done by
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using encode and decode appropriately or by using the utility functions
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force_text and force_bytes.
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It is recommended to use the utility functions for other string conversions.
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"""
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import six
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from six import binary_type
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from typing import Any, Dict, Mapping, Union, TypeVar, Text
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NonBinaryStr = TypeVar('NonBinaryStr', str, Text)
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# This is used to represent text or native strings
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def force_text(s, encoding='utf-8'):
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# type: (Union[Text, binary_type], str) -> Text
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"""converts a string to a text string"""
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if isinstance(s, Text):
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return s
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elif isinstance(s, binary_type):
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return s.decode(encoding)
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else:
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raise TypeError("force_text expects a string type")
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def force_bytes(s, encoding='utf-8'):
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# type: (Union[Text, binary_type], str) -> binary_type
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"""converts a string to binary string"""
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if isinstance(s, binary_type):
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return s
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elif isinstance(s, Text):
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return s.encode(encoding)
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else:
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raise TypeError("force_bytes expects a string type")
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def force_str(s, encoding='utf-8'):
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# type: (Union[Text, binary_type], str) -> str
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"""converts a string to a native string"""
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if isinstance(s, str):
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return s
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elif isinstance(s, Text):
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return s.encode(encoding)
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elif isinstance(s, binary_type):
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return s.decode(encoding)
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else:
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raise TypeError("force_str expects a string type")
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def dict_with_str_keys(dct, encoding='utf-8'):
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# type: (Mapping[NonBinaryStr, Any], str) -> Dict[str, Any]
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"""applies force_str on the keys of a dict (non-recursively)"""
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return {force_str(key, encoding): value for key, value in six.iteritems(dct)}
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class ModelReprMixin(object):
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"""
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This mixin provides a python 2 and 3 compatible way of handling string representation of a model.
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When declaring a model, inherit this mixin before django.db.models.Model.
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Define __unicode__ on your model which returns a typing.Text object.
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This mixin will automatically define __str__ and __repr__.
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"""
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def __unicode__(self):
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# type: () -> Text
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# Originally raised an exception, but Django (e.g. the ./manage.py shell)
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# was catching the exception and not displaying any sort of error
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return u"Implement __unicode__ in your subclass of ModelReprMixin!"
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def __str__(self):
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# type: () -> str
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return force_str(self.__unicode__())
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def __repr__(self):
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# type: () -> str
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return force_str(self.__unicode__())
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