The canonical data structure for this type of queries is a dictionary:
In [1]: t = (
...: ('P', 'Shtg1'),
...: ('R', u'Shtg2'),
...: ('D', 'Shtg3'),
...: )
In [2]: d = dict(t)
In [3]: d['P']
Out[3]: 'Shtg1'
If you use a tuple, there is no way to avoid looping (either explicit or implicit).
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