In Python how do I loop through the dictionary and change the value if it equals something

Question

If the value is None  I d like to change it to     empty string    I start off like this  but I forget   for k  v in mydict items        if v is None      right

User · Answer

You could create a dict comprehension of just the elements whose values are None, and then update back into the original:

tmp = dict((k,"") for k,v in mydict.iteritems() if v is None)
mydict.update(tmp)

Update - did some performance tests

Well, after trying dicts of from 100 to 10,000 items, with varying percentage of None values, the performance of Alex's solution is across-the-board about twice as fast as this solution.

User · Answer

for k  v in mydict iteritems        if v is None          mydict k         In a more general case  e g  if you were adding or removing keys  it might not be safe to change the structure of the container you re looping on -- so using items to loop on an independent list copy thereof might be prudent -- but assigning a different value at a given existing index does not incur any problem  so  in Python 2 any  it s better to use iteritems   In Python3 however the code gives AttributeError   dict  object has no attribute  iteritems  error  Use items   instead of iteritems   here    Refer to this post

User · Answer

Comprehensions are usually faster  and this has the advantage of not editing mydict during the iteration   mydict   dict  k  v if v else     for k  v in mydict items

[python] In Python, how do I loop through the dictionary and change the value if it equals something?

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