Does Python have a string contains substring method

Question

I m looking for a string contains or string indexof method in Python   I want to do   if not somestring contains  blah       continue

User · Answer

If it s just a substring search you can use string find  substring     You do have to be a little careful with find  index  and in though  as they are substring searches  In other words  this   s    This be a string  if s find  is      -1      print  No  is  here    else      print  Found  is  in the string      It would print Found  is  in the string  Similarly  if  is  in s  would evaluate to True  This may or may not be what you want

User · Answer

Does Python have a string contains substring method   99  of use cases will be covered using the keyword  in  which returns True or False   substring  in any string  For the use case of getting the index  use str find  which returns -1 on failure  and has optional positional arguments   start   0 stop   len any string  any string find  substring   start  stop   or str index  like find but raises ValueError on failure   start   100  end   1000 any string index  substring   start  end   Explanation Use the in comparison operator because  the language intends its usage  and other Python programmers will expect you to use it    gt  gt  gt   foo  in    foo    True  The opposite  complement   which the original question asked for  is not in   gt  gt  gt   foo  not in    foo      returns False False  This is semantically the same as not  foo  in    foo    but it s much more readable and explicitly provided for in the language as a readability improvement  Avoid using   contains   The  quot contains quot  method implements the behavior for in  This example  str   contains      foo      foo    returns True  You could also call this function from the instance of the superstring     foo      contains    foo    But don t  Methods that start with underscores are considered semantically non-public  The only reason to use this is when implementing or extending the in and not in functionality  e g  if subclassing str   class NoisyString str       def   contains   self  other           print f testing if  quot  other  quot  in  quot  self  quot            return super NoisyString  self    contains   other   ns   NoisyString  a string with a substring inside    and now   gt  gt  gt   substring  in ns testing if  quot substring quot  in  quot a string with a substring inside quot  True  Don t use find and index to test for  quot contains quot  Don t use the following string methods to test for  quot contains quot    gt  gt  gt     foo    index  foo   2  gt  gt  gt     foo    find  foo   2   gt  gt  gt     oo    find  foo   -1  gt  gt  gt     oo    index  foo    Traceback  most recent call last     File  quot  lt pyshell 40 gt  quot   line 1  in  lt module gt         oo    index  foo   ValueError  substring not found  Other languages may have no methods to directly test for substrings  and so you would have to use these types of methods  but with Python  it is much more efficient to use the in comparison operator  Also  these are not drop-in replacements for in  You may have to handle the exception or -1 cases  and if they return 0  because they found the substring at the beginning  the boolean interpretation is False instead of True  If you really mean not any string startswith substring  then say it  Performance comparisons We can compare various ways of accomplishing the same goal  import timeit  def in  s  other       return other in s  def contains s  other       return s   contains   other   def find s  other       return s find other     -1  def index s  other       try          s index other      except ValueError          return False     else          return True    perf dict      in True   min timeit repeat lambda  in   superstring    str       in False   min timeit repeat lambda  in   superstring    not         contains   True   min timeit repeat lambda  contains  superstring    str         contains   False   min timeit repeat lambda  contains  superstring    not       find True   min timeit repeat lambda  find  superstring    str       find False   min timeit repeat lambda  find  superstring    not       index True   min timeit repeat lambda  index  superstring    str       index False   min timeit repeat lambda  index  superstring    not         And now we see that using in is much faster than the others  Less time to do an equivalent operation is better   gt  gt  gt  perf dict   in True   0 16450627865128808    in False   0 1609668098178645      contains   True   0 24355481654697542      contains   False   0 24382793854783813    find True   0 3067379407923454    find False   0 29860888058124146    index True   0 29647137792585454    index False   0 5502287584545229

User · Answer

You can use regular expressions to get the occurrences    gt  gt  gt  import re  gt  gt  gt  print re findall r    t    to search in     searches for t or space   t         t

User · Answer

So apparently there is nothing similar for vector-wise comparison  An obvious Python way to do so would be   names     bob    john    mike   any st in  bob and john  for st in names    gt  gt  True  any st in  mary and jane  for st in names    gt  gt  False

User · Answer

Here is your answer   if  insert char or string here  in  insert string to search here        DOSTUFF   For checking if it is false   if not  insert char or string here  in  insert string to search here        DOSTUFF   OR   if  insert char or string here  not in  insert string to search here        DOSTUFF

User · Answer

in Python strings and lists Here are a few useful examples that speak for themselves concerning the in method   quot foo quot  in  quot foobar quot  True   quot foo quot  in  quot Foobar quot  False   quot foo quot  in  quot Foobar quot  lower   True   quot foo quot  capitalize   in  quot Foobar quot  True   quot foo quot  in   quot bar quot    quot foo quot    quot foobar quot   True   quot foo quot  in   quot fo quot    quot o quot    quot foobar quot   False    quot foo quot  in a for a in   quot fo quot    quot o quot    quot foobar quot     False  False  True   Caveat  Lists are iterables  and the in method acts on iterables  not just strings

User · Answer

If you are happy with  blah  in somestring but want it to be a function method call  you can probably do this  import operator  if not operator contains somestring   blah        continue   All operators in Python can be more or less found in the operator module including in

User · Answer

if needle in haystack  is the normal use  as  Michael says -- it relies on the in operator  more readable and faster than a method call   If you truly need a method instead of an operator  e g  to do some weird key  for a very peculiar sort       that would be  haystack    contains     But since your example is for use in an if  I guess you don t really mean what you say -    It s not good form  nor readable  nor efficient  to use special methods directly -- they re meant to be used  instead  through the operators and builtins that delegate to them

User · Answer

You can use the in operator   if  blah  not in somestring       continue

User · Answer

You can use y count     It will return the integer value of the number of times a sub string appears in a string   For example   string count  bah    gt  gt  0 string count  Hello    gt  gt  1

[python] Does Python have a string 'contains' substring method?

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