filter items in a python dictionary where keys contain a specific string

Question

I m a C coder developing something in python  I know how to do the following in C  and hence in C-like logic applied to python   but I m wondering what the  Python  way of doing it is   I have a dictionary d  and I d like to operate on a subset of the items  only those who s key  string  contains a specific substring   i e  the C logic would be   for key in d      if filter string in key            do something     else           do nothing  continue   I m imagining the python version would be something like  filtered dict   crazy python syntax d  substring  for key value in filtered dict iteritems          do something   I ve found a lot of posts on here regarding filtering dictionaries  but couldn t find one which involved exactly this   My dictionary is not nested and i m using python 2 7

User · Answer

input     A   a    B   b    C   c   output    k v for  k v  in input items   if key satifies condition k

User · Answer

Go for whatever is most readable and easily maintainable  Just because you can write it out in a single line doesn t mean that you should  Your existing solution is close to what I would use other than I would user iteritems to skip the value lookup  and I hate nested ifs if I can avoid them   for key  val in d iteritems        if filter string not in key          continue       do something   However if you realllly want something to let you iterate through a filtered dict then I would not do the two step process of building the filtered dict and then iterating through it  but instead use a generator  because what is more pythonic  and awesome  than a generator   First we create our generator  and good design dictates that we make it abstract enough to be reusable     The implementation of my generator may look vaguely familiar  no  def filter dict d  filter string       for key  val in d iteritems            if filter string not in key              continue         yield key  val   And then we can use the generator to solve your problem nice and cleanly with simple  understandable code       for key  val in filter dict d  some string         do something   In short  generators are awesome

User · Answer

How about a dict comprehension   filtered dict    k v for k v in d iteritems   if filter string in k    One you see it  it should be self-explanatory  as it reads like English pretty well   This syntax requires Python 2 7 or greater   In Python 3  there is only dict items    not iteritems   so you would use   filtered dict    k v for  k v  in d items   if filter string in k

User · Answer

Jonathon gave you an approach using dict comprehensions in his answer  Here is an approach that deals with your do something part   If you want to do something with the values of the dictionary  you don t need a dictionary comprehension at all   I m using iteritems   since you tagged your question with python-2 7  results   map some function    k v  for k v in a dict iteritems   if  foo  in k     Now the result will be in a list with some function applied to each key value pair of the dictionary  that has foo in its key   If you just want to deal with the values and ignore the keys  just change the list comprehension   results   map some function   v for k v in a dict iteritems   if  foo  in k     some function can be any callable  so a lambda would work as well   results   map lambda x  x 2   v for k v in a dict iteritems   if  foo  in k     The inner list is actually not required  as you can pass a generator expression to map as well    gt  gt  gt  map lambda a  a 0  a 1     k v  for k v in  2 2  3 2  iteritems   if k    2    4

User · Answer

You can use the built-in filter function to filter dictionaries  lists  etc  based on specific conditions   filtered dict   dict filter lambda item  filter str in item 0   d items       The advantage is that you can use it for different data structures

[python] filter items in a python dictionary where keys contain a specific string

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