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"""Tuples.
@see: https://www.w3schools.com/python/python_tuples.asp
@see: https://docs.python.org/3/tutorial/datastructures.html#tuples-and-sequences
A tuple is a collection which is ordered and unchangeable. In Python tuples are written with
round brackets.
The Tuples have following properties:
- You cannot change values in a tuple.
- You cannot remove items in a tuple.
"""
import pytest
def test_tuples():
"""Tuples"""
fruits_tuple = ("apple", "banana", "cherry")
assert isinstance(fruits_tuple, tuple)
assert fruits_tuple[0] == "apple"
assert fruits_tuple[1] == "banana"
assert fruits_tuple[2] == "cherry"
# You cannot change values in a tuple.
with pytest.raises(Exception):
# pylint: disable=unsupported-assignment-operation
fruits_tuple[0] = "pineapple"
# It is also possible to use the tuple() constructor to make a tuple (note the double
# round-brackets).
# The len() function returns the length of the tuple.
fruits_tuple_via_constructor = tuple(("apple", "banana", "cherry"))
assert isinstance(fruits_tuple_via_constructor, tuple)
assert len(fruits_tuple_via_constructor) == 3
# It is also possible to omit brackets when initializing tuples.
another_tuple = 12345, 54321, 'hello!'
assert another_tuple == (12345, 54321, 'hello!')
# Tuples may be nested:
nested_tuple = another_tuple, (1, 2, 3, 4, 5)
assert nested_tuple == ((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
# As you see, on output tuples are always enclosed in parentheses, so that nested tuples are
# interpreted correctly; they may be input with or without surrounding parentheses, although
# often parentheses are necessary anyway (if the tuple is part of a larger expression). It is
# not possible to assign to the individual items of a tuple, however it is possible to create
# tuples which contain mutable objects, such as lists.
# A special problem is the construction of tuples containing 0 or 1 items: the syntax has some
# extra quirks to accommodate these. Empty tuples are constructed by an empty pair of
# parentheses; a tuple with one item is constructed by following a value with a comma (it is
# not sufficient to enclose a single value in parentheses). Ugly, but effective. For example:
empty_tuple = ()
# pylint: disable=len-as-condition
assert len(empty_tuple) == 0
# pylint: disable=trailing-comma-tuple
singleton_tuple = 'hello', # <-- note trailing comma
assert len(singleton_tuple) == 1
assert singleton_tuple == ('hello',)
# The following example is called tuple packing:
packed_tuple = 12345, 54321, 'hello!'
# The reverse operation is also possible.
first_tuple_number, second_tuple_number, third_tuple_string = packed_tuple
assert first_tuple_number == 12345
assert second_tuple_number == 54321
assert third_tuple_string == 'hello!'
# This is called, appropriately enough, sequence unpacking and works for any sequence on the
# right-hand side. Sequence unpacking requires that there are as many variables on the left
# side of the equals sign as there are elements in the sequence. Note that multiple assignment
# is really just a combination of tuple packing and sequence unpacking.
# Swapping using tuples.
# Data can be swapped from one variable to another in python using
# tuples. This eliminates the need to use a 'temp' variable.
first_number = 123
second_number = 456
first_number, second_number = second_number, first_number
assert first_number == 456
assert second_number == 123