相反的Python字符串格式：从具有命名参数的字符串生成字典

Question

I have a string like this, where symbol and property vary:

a = '/stock/%(symbol)s/%(property)s'

I have another string like this, where AAPL and price vary:

b = '/stock/AAPL/price'

I'm trying to generate a dict like this:

c = {
    'symbol': 'AAPL',
    'property': 'price'
}

With string formatting, I could do a this:

> a % c == b
True

But I'm trying to go the other direction. Time for some regex magic?

Answer 1

A solution with regular expressions:

>>> import re
>>> b = '/stock/AAPL/price'
>>> result = re.match('/.*?/(?P<symbol>.*?)/(?P<property>.*)', b)
>>> result.groupdict()
{'symbol': 'AAPL', 'property': 'price'}

You can adjust a bit more the regular expression but, in essence, this is the idea.

Answer 2

Assuming well-behaved input, you could just split the strings and zip them to a dict

keys = ('symbol', 'property')
b = '/stock/AAPL/price'
dict(zip(keys, b.split('/')[2:4]))

Answer 3

This is similar to @moliware's solution, but there's no hard-coding of keys required in this solution:

import re

class mydict(dict):
    def __missing__(self, key):
        self.setdefault(key, '')
        return ''

def solve(a, b):
    dic = mydict()
    a % dic
    strs = a
    for x in dic:
        esc = re.escape(x)
        strs = re.sub(r'(%\({}\).)'.format(esc), '(?P<{}>.*)'.format(esc), strs)
    return re.search(strs, b).groupdict()

if __name__ == '__main__':
    a = '/stock/%(symbol)s/%(property)s'
    b = '/stock/AAPL/price'
    print solve(a, b)
    a = "Foo %(bar)s spam %(eggs)s %(python)s"
    b = 'Foo BAR spam 10 3.x'
    print solve(a, b)

Output:

{'symbol': 'AAPL', 'property': 'price'}
{'python': '3.x', 'eggs': '10', 'bar': 'BAR'}

As @torek pointed out for cases with ambiguous output(no space between keys) the answer can be wrong here.

For eg.

a = 'leading/%(A)s%(B)s/trailing'
b = 'leading/helloworld/trailing'

Here looking at just b it's hard to tell the actual value of either either A or B .