How to assert two list contain the same elements in Python

Question

When writing test cases  I often need to assert that two list contain the same elements without regard to their order   I have been doing this by converting the lists to sets   Is there any simpler way to do this   EDIT   As  MarkDickinson pointed out  I can just use TestCase assertItemsEqual   Notes that TestCase assertItemsEqual is new in Python2 7  If you are using an older version of Python  you can use unittest2 - a backport of new features of Python 2 7

User · Answer

Converting your lists to sets will tell you that they contain the same elements. But this method cannot confirm that they contain the same number of all elements. For example, your method will fail in this case:

L1 = [1,2,2,3]
L2 = [1,2,3,3]

You are likely better off sorting the two lists and comparing them:

def checkEqual(L1, L2):
    if sorted(L1) == sorted(L2):
        print "the two lists are the same"
        return True
    else:
        print "the two lists are not the same"
        return False

Note that this does not alter the structure/contents of the two lists. Rather, the sorting creates two new lists

User · Answer

Given  l1    a b  l2    b a    In Python    3 0  assertCountEqual l1  l2    True   In Python    2 7  the above function was named   assertItemsEqual l1  l2    True   In Python  lt  2 7  import unittest2 assertItemsEqual l1  l2    True   Via six module  Any Python version   import unittest import six class MyTest unittest TestCase       def test self           six assertCountEqual self  self l1  self l2    True

User · Answer

Slightly faster version of the implementation  If you know that most couples lists will have different lengths    def checkEqual L1  L2       return len L1     len L2  and sorted L1     sorted L2    Comparing     gt  gt  gt  timeit lambda  sorting  1 2 3    3 2 1    2 42745304107666  gt  gt  gt  timeit lambda  lensorting  1 2 3    3 2 1    2 5644469261169434   speed down not much  for large lists the difference tends to 0    gt  gt  gt  timeit lambda  sorting  1 2 3    3 2 1 0    2 4570400714874268  gt  gt  gt  timeit lambda  lensorting  1 2 3    3 2 1 0    0 9596951007843018   speed up

User · Answer

Needs ensure library but you can compare list by      ensure  1  2   contains only  2  1     This will not raise assert exception  Documentation of thin is really thin so i would recommend to look at ensure s codes on github

User · Answer

As of Python 3 2 unittest TestCase assertItemsEqual doc  has been replaced by unittest TestCase assertCountEqual doc  which does exactly what you are looking for  as you can read from the python standard library documentation  The method is somewhat misleadingly named but it does exactly what you are looking for      a and b have the same elements in the same number  regardless of their order   Here a simple example which compares two lists having the same elements but in a different order    using assertCountEqual the test will succeed using assertListEqual the test will fail due to the order difference of the two lists   Here a little example script   import unittest   class TestListElements unittest TestCase       def setUp self           self expected     foo    bar    baz           self result     baz    foo    bar        def test count eq self              Will succeed            self assertCountEqual self result  self expected       def test list eq self              Will fail            self assertListEqual self result  self expected   if   name         main         unittest main     Side Note   Please make sure that the elements in the lists you are comparing are sortable

[python] How to assert two list contain the same elements in Python?

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