是否有一种pythonic方法来进行带索引的while循环？

Question

Is there a more Pythonic way to write the code beneath, so that it iterates over some condition but also keeps an index of the iterations?

def TrieMatching(text, trie):
    match_locations = []
    location = 0
    while text:
        if PrefixTrieMatching(text, trie):
            match_locations.append(location)
        text = text[1:]
        location += 1

Answer 1

I'm always fond of list comprehensions.

def TrieMatching(text, trie):
    match_locations = [
        location
        for location in range(len(text))
        if PrefixTrieMatch(text[location:],trie)
    ]

Answer 2

You are always increasing i so just use range:

def TrieMatching(text, trie):
    match_locations = []
    for i in range(len(text)):
        if PrefixTrieMatching(text[i:], trie):
            match_locations.append(i)

Answer 3

Have you ever heard the old saying "Give a man a hammer and suddenly all his problems look like nails"? The while loop is not a hammer.

Why use a while loop at all? If I am correct your problem can be stated without reference to them as "produce a list of the locations of all suffixes of text which match a given trie ".

This can be written as a list comprehension:

def TrieMatching(text, trie):
   return [l for l in range(len(text)) if PrefixTrieMatching(text[l:], trie)]

I added a return as there is little point in computing a value only to retain no reference to it.

Answer 4

enumerate() is a great way to iterate over something and get an index as well. It returns an iterable that yields tuples of (counter, value)

https://docs.python.org/2/library/functions.html#enumerate

From the docs:

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]

So you can use it in a for loop really easily:

for (i,season) in enumerate(seasons):
     print "{} {}".format(i,season)

prints:

0 Spring
1 Summer
2 Fall
3 Winer

Answer 5

enumerate is often used for tracking the index in a for loop. Here is an example of how to use it.

for i, elem in enumerate("abc"):
    print(i, elem)

0 a
1 b
2 c

In your example, you aren't using the elem as in the above case, so enumerate may not be the best solution. You should probably either try using range or stick with the while loop you already have.

for location in range(len(text)):
    if PrefixTrieMatching(text[location:], trie):
        match_locations.append(location)

Answer 6

I wouldn't necessarily use this, but itertools.count() is [1, 2, 3, ...] .

import itertools
for i in itertools.count():
    ...