python - Populate dictionary from list in loop -

i have following code works fine , wondering how implement same logic using list comprehension.

def get_features(document, feature_space):     features = {}     w in feature_space:         features[w] = (w in document)     return features 

also going improvements in performance using list comprehension?

the thing both feature_space , document relatively big , many iterations run.

edit: sorry not making clear @ first, both feature_space , document lists.

• document list of words (a word may exist more once!)
• feature_space list of labels (features)

like this, dict comprehension:

def get_features(document, feature_space):     return {w: (w in document) w in feature_space} 

the features[key] = value expression becomes key: value part @ start, , rest of for loop(s) , if statements follow in nesting order.

yes, give performance boost, because you've removed features local name lookups , dict.__setitem__ calls.

note need make sure document data structure has fast membership tests. if list, convert set() first, example, ensure membership tests take o(1) (constant) time, not o(n) linear time of list:

def get_features(document, feature_space):     document = set(document)     return {w: (w in document) w in feature_space} 

with set, o(k) loop instead of o(kn) loop (where n size of document, k size of feature_space).