I have a list ['apple', 'banana', 'cherry']
I want to run map on it which will select a few items
l = map(lambda x : x if x == "apple" else pass, ['apple', 'banana', 'cherry'])
it seems that it should work but its giving syntax error
What is the issue here?
You probably need filter here and use lambda x : x == "apple".
Ex:
l = list(filter(lambda x : x == "apple", ['apple', 'banana', 'cherry']))
print(l)
l = [x for x in input if predicate(x)]you need this:
[x for x in ['apple', 'banana', 'cherry'] if x == "apple"]
pass is not a value, so you can't use it in an expression. You could use None, but then you end up with ['apple', None, None] rather than just ['apple'], so you have to filter the Nones like this:
l = filter(lambda x: x is not None, map(lambda x : x if x == "apple" else None, ['apple', 'banana', 'cherry']))
A cleaner solution would be to use list comprehension:
l = [ x for x in ['apple', 'banana', 'cherry'] if x == 'apple' ]
Depending on size of your list it might be better to use generator rather than list comprehension, that is:
l = (x for x in ['apple', 'banana', 'cherry'] if x=='apple')
generally list comprehensions will lead to bigger memory usage, than equivalent generators, though for small sizes difference might be neglible.
you are not allowed to use pass keyword in conditional expressions(ternary operator)
you can read more about conditional expressions in PEP308
So, if you want to use the map built-in function you have to pick an "else" value for the ternary operator, ex:
map(lambda x : x if x == "apple" else None, ['apple', 'banana', 'cherry'])
or if you want to filter your list by the string "apple" you can use @Rakesh suggested solution by using the built-in function filter:
list(filter(lambda x : x == "apple", ['apple', 'banana', 'cherry']))
passbranch? Note thatmapconverts every input element to an output element. It cannot remove elements.lambdato usemaporfilter, don't. It'll be slower and less readable than an equivalent list comprehension/generator expression that avoids alambdaby inlining the same logic.map/filter, listcomp, genexpr).