Case insensitive in

Question

I love using the expression  if  MICHAEL89  in USERNAMES            where USERNAMES is a list     Is there any way to match items with case insensitivity or do I need to use a custom method  Just wondering if there is a need to write extra code for this

User · Answer

Here s one way   if string1 lower   in string2 lower               For this to work  both string1 and string2 objects must be of type string

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You could do  matcher   re compile  MICHAEL89   re IGNORECASE  filter matcher match  USERNAMES     Update   played around a bit and am thinking you could get a better short-circuit type approach using  matcher   re compile  MICHAEL89   re IGNORECASE  if any  ifilter  matcher match  USERNAMES           your code here   The ifilter function is from itertools  one of my favorite modules within Python   It s faster than a generator but only creates the next item of the list when called upon

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My 5  wrong  cents      a  in    join   A    lower     UPDATE  Ouch  totally agree  jpp  I ll keep as an example of bad practice

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I would make a wrapper so you can be non-invasive   Minimally  for example      class CaseInsensitively object       def   init   self  s           self   s   s lower       def   hash   self           return hash self   s      def   eq   self  other             ensure proper comparison between instances of this class         try             other   other   s         except  TypeError  AttributeError             try               other   other lower             except               pass         return self   s    other   Now  if CaseInsensitively  MICHAEL89   in whatever  should behave as required  whether the right-hand side is a list  dict  or set     It may require more effort to achieve similar results for string inclusion  avoid warnings in some cases involving unicode  etc

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I needed this for a dictionary instead of list  Jochen solution was the most elegant for that case so I modded it a bit   class CaseInsensitiveDict dict           requests special dicts are case insensitive when using the in operator       this implements a similar behaviour        def   contains   self  name     implements  in          return name casefold   in  n casefold   for n in self keys      now you can convert a dictionary like so USERNAMESDICT   CaseInsensitiveDict USERNAMESDICT  and use if  MICHAEL89  in USERNAMESDICT

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I think you have to write some extra code  For example   if  MICHAEL89  in map lambda name  name upper    USERNAMES            In this case we are forming a new list with all entries in USERNAMES converted to upper case and then comparing against this new list   Update   As  viraptor says  it is even better to use a generator instead of map  See  Nathon s answer

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str casefold is recommended for case-insensitive string matching   nmichaels s solution can trivially be adapted   Use either   if  MICHAEL89  casefold   in  name casefold   for name in USERNAMES     Or   if  MICHAEL89  casefold   in map str casefold  USERNAMES     As per the docs      Casefolding is similar to lowercasing but more aggressive because it   is intended to remove all case distinctions in a string  For example    the German lowercase letter      is equivalent to  ss   Since it is   already lowercase  lower   would do nothing to       casefold     converts it to  ss

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To have it in one line  this is what I did   if any   True if  MICHAEL89  in username upper   else False for username in USERNAMES         print  username exists in list     I didn t test it time-wise though  I am not sure how fast efficient it is

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Usually  in oop at least  you shape your object to behave the way you want  name in USERNAMES is not case insensitive  so USERNAMES needs to change   class NameList object       def   init   self  names           self names   names      def   contains   self  name     implements  in          return name lower   in  n lower   for n in self names       def add self  name           self names append name     now this works usernames   NameList USERNAMES  print someone in usernames   The great thing about this is that it opens the path for many improvements  without having to change any code outside the class  For example  you could change the self names to a set for faster lookups  or compute the  n lower   for n in self names  only once and store it on the class and so on

User · Answer

username    MICHAEL89  if username upper   in  name upper   for name in USERNAMES             Alternatively   if username upper   in map str upper  USERNAMES             Or  yes  you can make a custom method

[python] Case insensitive 'in'

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