Python for and if on one line

Question

I have a issue with python   I make a simple list    gt  gt  gt  my list     one   two   three     I want create a  single line code  for find a string   for example  I have this code    gt  gt  gt    i  for i in my list if i   two     two     But when I watch the variable is wrong  I find the last value of my list     gt  gt  gt  print i three   Why does my variable contain the last element and not the element that I want to find

User · Answer

In list comprehension the loop variable i becomes global. After the iteration in the for loop it is a reference to the last element in your list.

If you want all matches then assign the list to a variable:

filtered =  [ i for i in my_list if i=='two']

If you want only the first match you could use a function generator

try:
     m = next( i for i in my_list if i=='two' )
except StopIteration:
     m = None

User · Answer

Found this one   x for  i x  in enumerate my list  if my list i      quot two quot    Will print    quot two quot

User · Answer

The reason it prints  quot three quot  is because you didnt define your array  The equivalent to what you re doing is  arr      for i in array       if i     quot two quot            arr push i  print i   You are asking for the last element it looked through  which is not what you should be doing  You need to be storing the array to a variable in order to get the element  The english equivalent of what you are doing is  You   quot I need you to print all the elements in this array that equal two  but in an array  And each time you cycle through the list  define the current element as I  quot  Computer   quot Here    quot two quot   quot  You   quot Now tell me  i  quot  Computer   quot  i  is equal to  quot three quot  You   quot Why  quot   The reason  i  is equal to  quot three quot  is because three was the last thing that was defined as I the computer did  i    quot one quot  i    quot two quot  i    quot three quot   print   quot two quot     Because you asked it to  If you want the index  go here If you want the values in an array  define the array  like this  MyArray     i  for i in my list if i   quot two quot

User · Answer

In python3 the variable i will be out of scope when you try to print it  To get the value you want you should store the result of your operation inside a new variable  my list     quot one quot   quot two quot   quot three quot   result   i  for i in my list if i   quot two quot   print result   you will then the following output   two

User · Answer

When you perform   gt  gt  gt    i  for i in my list if i   two     i is iterated through the list my list   As the list comprehension finishes evaluation  i is assigned to the last item in iteration  which is  three

User · Answer

You are producing a filtered list by using a list comprehension  i is still being bound to each and every element of that list  and the last element is still  three   even if it was subsequently filtered out from the list being produced   You should not use a list comprehension to pick out one element  Just use a for loop  and break to end it   for elem in my list      if elem     two           break   If you must have a one-liner  which would be counter to Python s philosophy  where readability matters   use the next   function and a generator expression   i   next  elem for elem in my list if elem     two    None    which will set i to None if there is no such matching element   The above is not that useful a filter  your are essentially testing if the value  two  is in the list  You can use in for that   elem    two  if  two  in my list else None

[python] Python for and if on one line

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