Find which dictionaries from a list contain word

问题

I have a dictionary with each keys having multiple values in a list. The tasks are:

To detect whether a given word is in the dictionary values
If it is true, then return the respective key from the dictionary

Task 1 is achieved by using an if condition:

if (word in dictionary[topics] for topics in dictionary.keys())

I want to get the topics when the if condition evaluates to be True. Something like

if (word in dictionary[topics] for topics in dictionary.keys()):
   print topics

回答1:

You can use a list comprehension (which is like a compressed for loop). They are simpler to write and can in some circumstances be faster to compute:

topiclist = [topic for topic in dictionary if word in dictionary[topic]]

You don't need dictionary.keys() because a dict is already an iterable object; iterating over it will yield the keys anyway, and (in Python 2) in a more efficient way than dictionary.keys().

EDIT: Here is another way to approach this (it avoids an extra dictionary look up):

topiclist = [topic for (topic, tlist) in dictionary.items() if word in tlist]

Avoiding the extra dictionary lookup may make it faster, although I haven't tested it.

In Python 2, for efficiency sake, you may want to do:

topiclist = [topic for (topic, tlist) in dictionary.iteritems() if word in tlist]

回答2:

if (word in dictionary[topics] for topics in dictionary.keys())

the problem with the above line is that you are creating a generator object that assesses whether word is in each value of dictionary and returning a bool for each. Since non-empty lists are always true, this if statement will ALWAYS be true, regardless if the word is in the values or not. you can do 2 things:

using any() will make your if statement work:

if any(word in dictionary[topics] for topics in dictionary.keys()):

however, this does not solve your initial problem of capturing the key value. so instead:

use an actual list comprehension that uses the predefined (I assume) variable word as a filter of sorts:
```
keys = [topics for topics in dictionary if word in dictionary[topics]]
```

use filter()

keys = filter(lambda key: word in dictionary[key],dictionary)

these both do the same thing. reminder that iterating through dictionary and dictionary.keys() are equivalent

just a note that both these methods return a list of all the keys that have values containing word. Access each key with regular list item getting.

回答3:

It sounds like the word you are searching for will be found in only one key. Correct?

If so, you can just iterate over the dictionary's key-value pairs until you find the key that contains the search word.

For Python 2:

found = False
for (topic, value) in dictionary.iteritems():
    if word in topic:
        found = True
        print topic
        break

For Python 3, just replace iteritems() with items().

来源：https://stackoverflow.com/questions/34004185/find-which-dictionaries-from-a-list-contain-word

标签

python

if-statement

for-loop

dictionary