How do I check that multiple keys are in a dict in a single pass

Question

I want to do something like  foo          foo   1       zip   2       zam   3       bar   4    if   quot foo quot    quot bar quot   in foo       do stuff  How do I check whether both foo and bar are in dict foo

User · Answer

Another option for detecting whether all keys are in a dict  dict to test              dict keys sought      quot key sought 1 quot    quot key sought 2 quot    quot key sought 3 quot       set  if keys sought  amp  dict to test keys      keys sought         True -- dict to test contains all keys in keys sought       code here     pass

User · Answer

In case you want to     also get the values for the keys check more than one dictonary   then   from operator import itemgetter foo     foo  1  zip  2  zam  3  bar  4  keys     foo   bar    getter   itemgetter  keys    returns all values try      values   getter foo  except KeyError        not both keys exist     pass

User · Answer

You can use  issubset   as well   gt  gt  gt    key1    key2   issubset   key1  1   key2  2   key3   3   True  gt  gt  gt    key4    key2   issubset   key1  1   key2  2   key3   3   False  gt  gt  gt

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While I like Alex Martelli s answer  it doesn t seem Pythonic to me   That is  I thought an important part of being Pythonic is to be easily understandable   With that goal   lt   isn t easy to understand   While it s more characters  using issubset   as suggested by Karl Voigtland s answer is more understandable   Since that method can use a dictionary as an argument  a short  understandable solution is   foo     foo   1   zip   2   zam   3   bar   4   if set   foo    bar    issubset foo        do stuff   I d like to use   foo    bar   in place of set   foo    bar     because it s shorter   However  it s not that understandable and I think the braces are too easily confused as being a dictionary

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Alex Martelli s solution set queries   lt   set my dict  is the shortest code but may not be the fastest  Assume Q   len queries  and D   len my dict    This takes O Q    O D  to make the two sets  and then  one hopes   only O min Q D   to do the subset test -- assuming of course that Python set look-up is O 1  -- this is worst case  when the answer is True    The generator solution of hughdbrown  et al   all k in my dict for k in queries  is worst-case O Q    Complicating factors   1  the loops in the set-based gadget are all done at C-speed whereas the any-based gadget is looping over bytecode   2  The caller of the any-based gadget may be able to use any knowledge of probability of failure to order the query items accordingly whereas the set-based gadget allows no such control   As always  if speed is important  benchmarking under operational conditions is a good idea

User · Answer

How about this   if all  key in foo for key in   foo   bar            do stuff     pass

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You don t have to wrap the left side in a set  You can just do this   if   foo    bar    lt   set some dict       pass   This also performs better than the all k in d     solution

User · Answer

gt  gt  gt  ok   five    5    two    2    one    1     gt  gt  gt  if   two  and  one  and  five   in ok        print  cool       cool   This seems to work

User · Answer

I think this is the smartest and pithonic     key1   key2    lt   my dict keys

User · Answer

In the case of determining whether only some keys match  this works    any keys i seek     key1    key2    key3    if set my dict  intersection any keys i seek         code here     pass   Yet another option to find if only some keys match    any keys i seek     key1    key2    key3    if any keys i seek  amp  my dict keys          code here     pass

User · Answer

How about using lambda    if reduce   lambda x  y  x and foo has key y       True   foo    bar        do stuff

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gt  gt  gt  if  foo  in foo and  bar  in foo          print  yes       yes   Jason     aren t necessary in Python

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Not to suggest that this isn t something that you haven t thought of  but I find that the simplest thing is usually the best   if   foo  in foo  and   bar  in foo         do stuff

User · Answer

Simple benchmarking rig for 3 of the alternatives   Put in your own values for D and Q       from timeit import Timer     setup    from random import randint as R d dict  str R 0 1000000   R 0 1000000   for i in range D   q dict  str R 0 1000000   R 0 1000000   for i in range Q   print  looking for  s items in  s   len q  len d            Timer  set q   lt   set d    D 1000000 Q 100   setup  timeit 1  looking for 100 items in 632499 0 28672504425048828   This one only works for Python3     Timer  set q   lt   d keys     D 1000000 Q 100   setup  timeit 1  looking for 100 items in 632084 2 5987625122070312e-05      Timer  all k in d for k in q    D 1000000 Q 100   setup  timeit 1  looking for 100 items in 632219 1 1920928955078125e-05

User · Answer

check for existence of all keys in a dict    key 1    key 2    key 3    lt   set my dict   check for existence of one or more keys in a dict    key 1    key 2    key 3    amp  set my dict

User · Answer

Using sets   if set   foo    bar    issubset foo        do stuff   Alternatively   if set   foo    bar     lt   set foo        do stuff

User · Answer

Well  you could do this    gt  gt  gt  if all  k in foo for k in   foo   bar             print  They re there       They re there

User · Answer

Just my take on this  there are two methods that are easy to understand of all the given options  So my main criteria is have very readable code  not exceptionally fast code  To keep code understandable  i prefer to given possibilities    var  lt   var2 keys   var issubset var2    The fact that  var  lt   var2 keys    executes faster in my testing below  i prefer this one   import timeit  timeit timeit  var  lt   var2 keys     setup  var   managed ip    hostname    fqdn    var2    zone    test-domain1 var23 com    hostname    bakje    api client ip    127 0 0 1    request data        request method    GET    request url    hvar2p   127 0 0 1 5000 test-domain1 var23 com bakje    utc datetime    04-Apr-2019 07 01 10    fqdn    bakje test-domain1 var23 com    var   managed ip    hostname    fqdn     0 1745898080000643  timeit timeit  var issubset var2    setup  var   managed ip    hostname    fqdn    var2    zone    test-domain1 var23 com    hostname    bakje    api client ip    127 0 0 1    request data        request method    GET    request url    hvar2p   127 0 0 1 5000 test-domain1 var23 com bakje    utc datetime    04-Apr-2019 07 01 10    fqdn    bakje test-domain1 var23 com    var   managed ip    hostname    fqdn      0 2644960229999924

User · Answer

if   foo    bar    lt   myDict keys          If you re still on Python 2  you can do  if   foo    bar    lt   myDict viewkeys          If you re still on a really old Python  lt   2 6  you can call set on the dict  but it ll iterate over the whole dict to build the set  and that s slow   if set   foo    bar     lt   set myDict

[python] How do I check that multiple keys are in a dict in a single pass?

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