Question

For a Python Dictionary with a tuple key, how can only the part of the dictionary with one of the tuple elements set to a single value be displayed. Then also looking to delete those elements.

For example, the dictionary

testTrak = {(0,1): '+', (0,2): '-', (1,1): '34.0', (1,2): 'test'}

and I want to list only the elements with the first number of the tuple = 1; that is, I want to list only (1,*) where the asterisk represents a wild card; hence, only
(1,1): '34.0' and (1,2): 'test' would be listed.

It seems maybe some kind of slicing should work but don’t see it.

Answer 1

Sorry, I misread your question. Here’s the solution you need for pretty much any Python version:

>>> testTrak = {(0,1): '+', (0,2): '-', (1,1): '34.0', (1,2): 'test'}
>>> dict([(key, value) for key, value in testTrak.items() if key[0] == 1])
{(1, 2): 'test', (1, 1): '34.0'}

In Python 2.7+ you can write the less verbose version:

>>> testTrak = {(0,1): '+', (0,2): '-', (1,1): '34.0', (1,2): 'test'}
>>> {key:value for key, value in testTrak.items() if key[0] == 1}
{(1, 2): 'test', (1, 1): '34.0'}

Excluding the items is just a matter negating the if clause, if this is what you asked in the comments:

>>> testTrak = {(0,1): '+', (0,2): '-', (1,1): '34.0', (1,2): 'test'}
>>> {key:value for key, value in testTrak.items() if key[0] != 1}
{(0, 1): '+', (0, 2): '-'}