Given the list ['a','ab','abc','bac'], I want to compute a list with strings that have 'ab' in them. I.e. the result is ['ab','abc']. How can this be done in Python?
Best Answer
This simple filtering can be achieved in many ways with Python. The best approach is to use "list comprehensions" as follows:
>>> lst = ['a', 'ab', 'abc', 'bac']>>> [k for k in lst if 'ab' in k]['ab', 'abc']Another way is to use the filter function. In Python 2:
>>> filter(lambda k: 'ab' in k, lst)['ab', 'abc']In Python 3, it returns an iterator instead of a list, but you can cast it:
>>> list(filter(lambda k: 'ab' in k, lst))['ab', 'abc']Though it's better practice to use a comprehension.
[x for x in L if 'ab' in x]# To support matches from the beginning, not any matches:items = ['a', 'ab', 'abc', 'bac']prefix = 'ab'filter(lambda x: x.startswith(prefix), items)Tried this out quickly in the interactive shell:
>>> l = ['a', 'ab', 'abc', 'bac']>>> [x for x in l if 'ab' in x]['ab', 'abc']>>>Why does this work? Because the in operator is defined for strings to mean: "is substring of".
Also, you might want to consider writing out the loop as opposed to using the list comprehension syntax used above:
l = ['a', 'ab', 'abc', 'bac']result = []for s in l:if 'ab' in s:result.append(s)mylist = ['a', 'ab', 'abc']assert 'ab' in mylist