Python String filter

Question

I am trying to solve a class assignment as listed below

Use lambda expressions and the filter() function to filter out words from a list that don't start with the letter 's'. For example:

seq = ['soup','dog','salad','cat','great']

should be filtered down to:

['soup','salad']

I wrote the following two sets of code...

seq = ['soup', 'dog','salad', 'cat', 'great']
result = filter (lambda test: test[0] == "s",seq)
print (result)

seq = ['soup', 'dog','salad', 'cat', 'great']
def checkf (input):
    if input[0]=='s':
            a = "TRUE"
    return(a)
test = seq[0]
result = filter (checkf(test),seq)
print (result)

Both codes give a strange answer filter object at 0x112aa06d8 as if it is returning a memory address in hexadecimal... What's wrong?

I have edited your question to more appropriately reflect a more readable question see https://stackoverflow.com/help/how-to-ask for further help in regards to asking — Tyler Cowan, Jan 25 '18 at 23:55
Possible duplicate of [Why does foo = filter(...) return a , not a list?](https://stackoverflow.com/questions/33174276/why-does-foo-filter-return-a-filter-object-not-a-list) — cowbert, Jan 25 '18 at 23:58
In Python 3, `filter` returns a special filter object rather than a list. You can convert it to a list using the `list` function. — khelwood, Jan 25 '18 at 23:58
what is wrong with the first code. Works for me with python 2. — Monish K Nair, Jan 26 '18 at 00:00
Possible duplicate of [How to use filter, map, and reduce in Python 3](https://stackoverflow.com/questions/13638898/how-to-use-filter-map-and-reduce-in-python-3) — melwil, Jan 26 '18 at 00:00

score 3 · Accepted Answer · edited Jan 25 '18 at 23:59

3

In python 3, filter objects are iterators. To print the contents, you have to materialize it into a sequence first, so try:

print( list(result))

See also: How to use filter, map, and reduce in Python 3

edited Jan 25 '18 at 23:59

melwil

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answered Jan 25 '18 at 23:57

cowbert

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Leda Grasiele · Answer 2 · 2019-01-10T00:52:57.667

To use lambda and filter to resolve this problem, you need to specify that the result of your code will be a list.

So the following will work:

seq = ['soup', 'dog','salad', 'cat', 'great']
list(filter (lambda test: test[0] == "s",seq))

or (assigning to an object):

seq = ['soup', 'dog','salad', 'cat', 'great']
result = list(filter (lambda test: test[0] == "s",seq))
print(result)

The result of the two codes will be:

['soup', 'salad']

score 0 · Answer 3 · edited Sep 09 '19 at 18:01

This is the below code where your seq can be solved according to the lambda function.

seq = ['soup', 'dog','salad', 'cat', 'great']
result = list(filter (lambda test: test[0] == "s",seq))
print(result)

output: ['soup', 'salad']

using it in a function

seq = ['soup', 'dog','salad', 'cat', 'great']
def check(input):
    result = list(filter (lambda test: test[0] == "s",seq))
    return result

check(seq)

output: ['soup', 'salad']

Python String filter

3 Answers3