How to avoid RuntimeError dictionary changed size during iteration error

Question

I have checked all of the other questions with the same error yet found no helpful solution     I have a dictionary of lists   d     a    1    b    1  2    c        d        in which some of the values are empty  At the end of creating these lists  I want to remove these empty lists before returning my dictionary  Current I am attempting to do this as follows   for i in d      if not d i           d pop i    however  this is giving me the runtime error  I am aware that you cannot add remove elements in a dictionary while iterating through it   what would be a way around this then

User · Answer

This worked for me     dict    1   a   2      3   b   4      5      6   c   for key  value in list dict items         if  value                 del dict key  print dict    dict    1   a   3   b   6   c       Casting the dictionary items to list creates a list of its items  so you can iterate over it and avoid the RuntimeError

User · Answer

The reason for the runtime error is that you cannot iterate through a data structure while its structure is changing during iteration   One way to achieve what you are looking for is to use list to append the keys you want to remove and then use pop function on dictionary to remove the identified key while iterating through the list   d     a    1    b    1  2    c        d      pop list       for i in d          if not d i                   pop list append i   for x in pop list          d pop x  print  d

User · Answer

For Python 3    k v for k v in d items   if v

User · Answer

Python 3 does not allow deletion while iterating  using for loop above  dictionary  There are various alternatives to do  one simple way is the to change following line   for i in x keys      With   for i in list x

User · Answer

For situations like this  i like to make a deep copy and loop through that copy while modifying the original dict   If the lookup field is within a list  you can enumerate in the for loop of the list and then specify the position as index to access the field in the original dict

User · Answer

dictc   quot stName quot   quot asas quot   keys dictc keys   for key in list keys       dictc key upper      New value  print str dictc

User · Answer

In Python 3 x and 2 x you can use use list to force a copy of the keys to be made  for i in list d    In Python 2 x calling keys made a copy of the keys that you could iterate over while modifying the dict  for i in d keys     But note that in Python 3 x this second method doesn t help with your error because keys returns an a view object instead of copynig the keys into a list

User · Answer

I would try to avoid inserting empty lists in the first place  but  would generally use   d    k  v for k v in d iteritems   if v    re-bind to non-empty   If prior to 2 7   d   dict   k  v  for k v in d iteritems   if v     or just   empty key vals   list k for k in k v in d iteritems   if v  for k in empty key vals      del k

User · Answer

Just use dictionary comprehension to copy the relevant items into a new dict   gt  gt  gt  d   a    1    c        b    1  2    d        gt  gt  gt  d     k   v for k v in d iteritems   if v   gt  gt  gt  d   a    1    b    1  2     For this in Python 3    gt  gt  gt  d   a    1    c        b    1  2    d        gt  gt  gt  d     k   v for k v in d items   if v   gt  gt  gt  d   a    1    b    1  2

User · Answer

You only need to use  copy    On that s way you iterate over the original dictionary fields and on the fly can change the desired dict  d dict   It s work on each python version  so it s more clear   In  1   d     a    1    b    1  2    c        d       In  2   for i in d copy                if not d i                   d pop i                    In  3   d Out 3     a    1    b    1  2

User · Answer

You cannot iterate through a dictionary while its changing during for loop  Make a casting to list and iterate over that list  it works for me       for key in list d           if not d key                d pop key

[python] How to avoid "RuntimeError: dictionary changed size during iteration" error?

Examples related to python

Examples related to list

Examples related to dictionary

Examples related to loops