How to get the index in the 'in' statement in Python

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Finding the index of an item given a list containing it in Python 23 answers

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要避免一个循环，可以使用try-except子句（不使用if ... in ...:

try:
    i = vocab.index(word)
except ValueError as e:
    print e # Optional
    i = -1

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This is a case where I wish I could do assignment in an if statement, but I can't so this is the solution:

If vocab is a list :

try:
    index = vocab.index(word)
except ValueError:
    pass
else:
    print index, word

if vocab is a str :

index = vocab.find(word)
if index >= 0:
    print index, word

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def getindex(iterable,target):
    for idx,value in enumerate(iterable):
        if value==target: return idx
    return -1

Note that this WILL NOT work if you're trying to find a substring in a string (as I'm assuming, since you're doing if word in vocab . In that case you really should do:

try: idx = iterable.index(target)
except ValueError as e: # Not found
    # Handle it

If you try to use the getindex function above, it will always return -1 for any value len(target) > 1 since it will break your iterable into its smallest iteration, which is by-letter for strings.

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