Put your code in functions. Maybe this is pedantic, but it's not really an
algorithm if you cannot reuse it. If the logic is floating around with
various setup and printing code, it's not reusable in any convenient sense.
Your demo code isn't doing what you think it's doing. Comment out the sorting
code, and the printed result is the same: the month names in proper order. Why?
Because sorted_list is being driven by the ordering of the months dict, not
the we-hope-its-sorted L1. As an experiment, move January to the end of that
dict, and watch what happens.
# The order of sorted_list is not affected by whether L1 is sorted.
sorted_list = [k for k, v in months.items() if v in L1]
Even if it were fixed, your demo code is not well-suited to the problem at hand
-- checking whether your sort algorithm is correct. Instead, your demo code is
good for addressing a different question: how to sort dict keys based on dict
values. Here's one way:
# Sorting dict keys based on dict values -- a different question.
sorted_names = sorted(months, key = lambda name: months[name])
A better way to test your sorting algorithm is to shuffle the values, sort them
with your algorithm, and check your sorted list against what the Python
sort() function gives us. It's easy to write and a good way to check many
more cases than anything you could manually type. Here's one illustration of
how you might check it. You could easily wrap a loop around this kind of
testing to include a wider range of list sizes (including edge cases like vals = [] or vals = [1]).
from random import shuffle
def main():
# Some data that needs sorting.
vals = list(range(1, 13))
shuffle(vals)
# Sort both ways and compare.
expected = sorted(vals)
selection_sort(vals)
if vals != expected:
print('GOT', vals)
print('EXP', expected)
def selection_sort(L1):
# L1 is a non-standard Python variable name. In a general sorting
# function, where you have no idea what the values represent,
# an idiomatic name would be xs (one x, many xs).
for i in range(1,len(L1)):
j = 0
if L1[j] > L1[i] :
L1[j], L1[i] = L1[i] ,L1[j]
if __name__ == '__main__':
main()
Your sorting algorithm isn't working. Here's output from one run:
GOT [1, 7, 8, 4, 12, 10, 2, 11, 6, 5, 9, 3]
EXP [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
If you add these suggestions to your code, and do some debugging work, I'm sure
you'll figure out a correct implementation. For example, you are not finding
the index of the minimum value in the rest of the list -- a key concept in
Wikpedia's description of selection
sort. Come back for another code
review after you have another draft.
