旧版python的OrderedDict

Question

Ordered dictionaries are extremely useful structures, but unfortunately these are quite recent only working in versions from 3.1 and 2.7 . How can I use an ordered dictionary in older versions?

Answer 1

我用pip在python 2.6上安装了ordereddict

pip install ordereddict

Answer 2

According to the documentation , for Python versions 2.4 or later this code should be used. There is also some code from Raymond Hettinger , one of the contributors to the PEP . The code here is claimed to work under 2.6 and 3.0 and was made for the proposal.

Answer 3

To import a OrderedDict class for different versions of Python, consider this snippet:

try:
    from collections import OrderedDict
except ImportError:
    from ordereddict import OrderedDict

# Now use it from any version of Python
mydict = OrderedDict()

Versions older than Python 2.6 will need to install ordereddict (using pip or other methods), but newer versions will import from the built-in collections module.

Answer 4

Also, you could just program your way around it if your situation allows:

def doSomething(strInput): return [ord(x) for x in strInput]

things = ['first', 'second', 'third', 'fourth']

oDict = {}
orderedKeys = []
for thing in things:
    oDict[thing] = doSomething(thing)
    orderedKeys.append(thing)

for key in oDict.keys():
    print key, ": ", oDict[key]

print

for key in orderedKeys:
    print key, ": ", oDict[key]

second : [115, 101, 99, 111, 110, 100]
fourth : [102, 111, 117, 114, 116, 104]
third : [116, 104, 105, 114, 100]
first : [102, 105, 114, 115, 116]

first : [102, 105, 114, 115, 116]
second : [115, 101, 99, 111, 110, 100]
third : [116, 104, 105, 114, 100]
fourth : [102, 111, 117, 114, 116, 104]

You could embed the ordered keys in your Dictionary too, I suppose, as oDict['keyList'] = orderedKeys

Answer 5

Also you can try future , py2-3 compatible codebase:

1. install future via pip:

pip install future

2. import and use OrderedDict:

from future.moves.collections import OrderedDict

source

Answer 6

in python2.6 gave to me:

$ pip install ordereddict
  Could not find a version that satisfies the requirement from (from versions:)
No matching distribution found for from

but

$ easy_install ordereddict
install_dir /usr/local/lib/python2.6/dist-packages/
Searching for ordereddict
Reading http://pypi.python.org/simple/ordereddict/
Best match: ordereddict 1.1
Downloading https://pypi.python.org/packages/source/o/ordereddict/ordereddict-1.1.tar.gz#md5=a0ed854ee442051b249bfad0f638bbec
Processing ordereddict-1.1.tar.gz
Running ordereddict-1.1/setup.py -q bdist_egg --dist-dir /tmp/easy_install-lYgPE3/ordereddict-1.1/egg-dist-tmp-GF2v6g
zip_safe flag not set; analyzing archive contents...
Adding ordereddict 1.1 to easy-install.pth file

Installed /usr/local/lib/python2.6/dist-packages/ordereddict-1.1-py2.6.egg
Processing dependencies for ordereddict
Finished processing dependencies for ordereddict

did.

Answer 7

For those who can't depend on the user having pip for some reason, here is a really terrible implementaiton of OrderedDict (it is immutable, has most of the features but none of the performance boost).

class OrderedDict(tuple):
    '''A really terrible implementation of OrderedDict (for python < 2.7)'''
    def __new__(cls, constructor, *args):
        items = tuple(constructor)
        values = tuple(n[1] for n in items)
        out = tuple.__new__(cls, (n[0] for n in items))
        out.keys = lambda: out
        out.items = lambda: items
        out.values = lambda: values
        return out

    def __getitem__(self, key):
        try:
            return next(v for (k, v) in self.items() if k == key)
        except:
            raise KeyError(key)