How to report an error if an element is missing in the list of lists

Question

suppose

list1 = [[\'a\', (1, 1)], [\'a\', (1, 3)], [\'a\', (1, 4)], [\'b\', (2,1)], [\'b\', (2,2)], [\'b\',(2, 4)]]

list2 = [[(1, 1), (1, 3), (2, 1), (2, 2), (         


        

Answer 1

You should use a dict instead of a list. But here's a solution using your structures. s1 is a similar idea as the previous answer but note the unnecessarily long list comprehension to get the pattern you have in list1. And you require a specific for loop to check rather than the set "-" operator.

>>> s1 = [[x, (c, d)] for x in ['a', 'b']
...                   for c in range(1, 3)
...                   for d in range(1, 5)
...                   if x=='a' and c==1 or x=='b' and c==2]
>>> s1
[['a', (1, 1)], ['a', (1, 2)], ['a', (1, 3)], ['a', (1, 4)],
 ['b', (2, 1)], ['b', (2, 2)], ['b', (2, 3)], ['b', (2, 4)]]
>>>
>>> list1 = [['a', (1, 1)], ['a', (1, 3)], ['a', (1, 4)],
...          ['b', (2, 1)], ['b', (2, 2)], ['b', (2, 4)]]
>>> for thing in s1:
...     if thing not in list1:
...         print 'missing: ', thing
...         # or raise an error if you want
...         
missing:  ['a', (1, 2)]
missing:  ['b', (2, 3)]

Repeat the same for list2. Creating s2 should be easier using the example for s1 above.

Btw, the dict would look like this for list1:

dict1 = {'a': [(1, 1), (1, 3), (1, 4)], 'b': [(2, 1), (2, 2), (2, 4)]}

Then creating s1 is simplified a bit and but the comparison loop might get two lines longer.

---

To answer your question to generalize, then either 1. knowing letters first or 2. knowing numbers/number of letters?

Knowing letters:

>>> set_of_letters = ('a', 'b', 'c')
>>> s1 = [[x, (ord(x)-96, d)]
...       for x in set_of_letters
...       for d in range(1, 5)]
>>> s1
[['a', (1, 1)], ['a', (1, 2)], ['a', (1, 3)], ['a', (1, 4)],
 ['b', (2, 1)], ['b', (2, 2)], ['b', (2, 3)], ['b', (2, 4)],
 ['c', (3, 1)], ['c', (3, 2)], ['c', (3, 3)], ['c', (3, 4)]]

Knowing numbers:

>>> number_of_letters = 3
>>> s1 = [[chr(c+96), (c, d)]
...       for c in range(1, number_of_letters + 1)
...       for d in range(1, 5)]
>>> s1
[['a', (1, 1)], ['a', (1, 2)], ['a', (1, 3)], ['a', (1, 4)],
 ['b', (2, 1)], ['b', (2, 2)], ['b', (2, 3)], ['b', (2, 4)],
 ['c', (3, 1)], ['c', (3, 2)], ['c', (3, 3)], ['c', (3, 4)]]