Hal Lawrence - 1 year ago 89
Python Question

# Consecutive values?

Learning python, but having trouble telling function to find consecutive locations with same values. When I run the code, there's no errors but gives out the incorrect output. Suggestions on what to change?

``````def same_values(xs):
same = False
for i in (xs):
if xs == xs[1:]:
same = True
else:
return same
same_values('Misses') # This should return as true
``````

So you are looking for a consecutive pair in the list and returning true if you find one.

``````def same_values(xs):
for i in range(len(xs)-1):
if xs[i] == xs[i+1]:
return True
return False

>>> same_values('misses')
True
>>> same_values('mises')
False
``````

Would give you the correct answer.
However python has a powerful iterator algebra. The advantage of this is that it would work with iterators (iterators don't generally support `len()`) as well as lists:

``````import itertools as it

def same_values(xs):
a, b = it.tee(xs)
next(b, None)
return any(x == y for x, y in zip(a, b))
``````

This pattern is described in the `itertools` recipes as `pairwise`:

``````import itertools as it

def pairwise(iterable):
"s -> (s0,s1), (s1,s2), (s2, s3), ..."
a, b = it.tee(iterable)
next(b, None)
return zip(a, b)

def same_values(xs):
return any(x == y for x, y in pairwise(xs))
``````

For example to check if any 2 consecutive lines in a file are the same (this wouldn't work with the `list` version):

``````with open('somefile') as f:
print(same_values(f))
``````
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