Fastest way to convert a dict's keys & values from `unicode` to `str`?

问题

I'm receiving a dict from one "layer" of code upon which some calculations/modifications are performed before passing it onto another "layer". The original dict's keys & "string" values are unicode, but the layer they're being passed onto only accepts str.

This is going to be called often, so I'd like to know what would be the fastest way to convert something like:

{ u'spam': u'eggs', u'foo': True, u'bar': { u'baz': 97 } }

...to:

{ 'spam': 'eggs', 'foo': True, 'bar': { 'baz': 97 } }

...bearing in mind the non-"string" values need to stay as their original type.

Any thoughts?

回答1:

DATA = { u'spam': u'eggs', u'foo': frozenset([u'Gah!']), u'bar': { u'baz': 97 },
         u'list': [u'list', (True, u'Maybe'), set([u'and', u'a', u'set', 1])]}

def convert(data):
    if isinstance(data, basestring):
        return str(data)
    elif isinstance(data, collections.Mapping):
        return dict(map(convert, data.iteritems()))
    elif isinstance(data, collections.Iterable):
        return type(data)(map(convert, data))
    else:
        return data

print DATA
print convert(DATA)
# Prints:
# {u'list': [u'list', (True, u'Maybe'), set([u'and', u'a', u'set', 1])], u'foo': frozenset([u'Gah!']), u'bar': {u'baz': 97}, u'spam': u'eggs'}
# {'bar': {'baz': 97}, 'foo': frozenset(['Gah!']), 'list': ['list', (True, 'Maybe'), set(['and', 'a', 'set', 1])], 'spam': 'eggs'}

Assumptions:

You've imported the collections module and can make use of the abstract base classes it provides
You're happy to convert using the default encoding (use data.encode('utf-8') rather than str(data) if you need an explicit encoding).

If you need to support other container types, hopefully it's obvious how to follow the pattern and add cases for them.

回答2:

I know I'm late on this one:

def convert_keys_to_string(dictionary):
    """Recursively converts dictionary keys to strings."""
    if not isinstance(dictionary, dict):
        return dictionary
    return dict((str(k), convert_keys_to_string(v)) 
        for k, v in dictionary.items())

回答3:

If you wanted to do this inline and didn't need recursive descent, this might work:

DATA = { u'spam': u'eggs', u'foo': True, u'bar': { u'baz': 97 } }
print DATA
# "{ u'spam': u'eggs', u'foo': True, u'bar': { u'baz': 97 } }"

STRING_DATA = dict([(str(k), v) for k, v in data.items()])
print STRING_DATA
# "{ 'spam': 'eggs', 'foo': True, 'bar': { u'baz': 97 } }"

回答4:

def to_str(key, value):
    if isinstance(key, unicode):
        key = str(key)
    if isinstance(value, unicode):
        value = str(value)
    return key, value

pass key and value to it, and add recursion to your code to account for inner dictionary.

回答5:

for a non-nested dict (since the title does not mention that case, it might be interesting for other people)

{str(k): str(v) for k, v in my_dict.items()}

回答6:

To make it all inline (non-recursive):

{str(k):(str(v) if isinstance(v, unicode) else v) for k,v in my_dict.items()}

来源：https://stackoverflow.com/questions/1254454/fastest-way-to-convert-a-dicts-keys-values-from-unicode-to-str

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python

casting

types