Python Language Tuple: Difference between revisions

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==Tuple Concatenation with <tt>*</tt>==
==Tuple Concatenation with <tt>*</tt>==
Multiplying the tuple by an integer has the effect of concatenating that many copies of the tuple.
Multiplying the tuple by an integer has the effect of concatenating that many copies of the tuple.
<syntaxhighlight lang='py'>
t = (1, 2) * 3 #  (1, 2, 1, 2, 1, 2)
t = (1, 2) * 3 #  (1, 2, 1, 2, 1, 2)
</syntaxhighlight>
</syntaxhighlight>
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a, b, *_ = values
a, b, *_ = values
</syntaxhighlight>
</syntaxhighlight>
=Slices=
The same rule as for lists apply: {{Internal|Slicing_Lists_and_Tuples_in_Python#Overview|Slicing Lists and Tuples in Python}}


=Named Tuples=
=Named Tuples=
Named tuples can be a simple alternative to objects.
Named tuples can be a simple alternative to objects.
=Tuple Methods=
==<tt>count(val)</tt>==
Counts the number of occurrences of the given value.

Latest revision as of 21:48, 16 May 2024

Internal

TODO

  • TO PROCESS: PyOOP "Tuples and named tuples", "Named tuples"

Overview

A tuple is a immutable sequence type that contains zero or more elements and whose elements can be of different types. Once a tuple is defined, you can't add, delete or change items. A tuple is similar to a constant list, and could be used instead of a list, if we can afford the "list" to be immutable. Naturally, the list's mutating functions append(), insert() do not exist on tuples. There are several advantages of using a tuple instead of a list: a tuple uses less space than a list and they cannot be mutated by mistake. Positional function arguments can be grouped together and provided as a tuple in the function body (*args).

Declaration

A tuple is declared by specifying commas after each of its elements, with the exception of the empty tuple, that uses ():

empty_tuple = ()
one_element_tuple = 1,  # the trailing comma is mandatory
two_element_tuple = 1,2,   # for two or more elements, the trailing comma is optional

For aesthetic reasons, and also to make the tuple more visible, the comma-driven declaration can be enclosed in optional parentheses:

empty_tuple = ()
one_element_tuple = (1,)  # the trailing comma is mandatory
two_element_tuple = (1,2,)  # for two or more elements, the trailing comma is optional

Access a Tuple

To access the elements of a tuple, use the same bracket notation as for a list. The index is 0-based:

t = ('a', 'b', 'c')
assert 'a' == t[0]

Conversion from other Data Structures with tuple()

The tuple() converts lists, or iterables, in general, to tuples:

l = ['a', 'b', 'c']
t = tuple(l)
print(t)
assert 'a' == t[0]
assert 'b' == t[1]
assert 'c' == t[2]

Tuple Concatenation

Tuple Concatenation with +

Tuples can be concatenate with the + operator:

t = (1, 2, 3) + (4, 5)

Tuple Concatenation with *

Multiplying the tuple by an integer has the effect of concatenating that many copies of the tuple.

t = (1, 2) * 3 #  (1, 2, 1, 2, 1, 2)

Tuple Unpacking

Assigning multiple variable at once is called "tuple unpacking":

t = (1, 'B', 3.0)
a, b, c = t
print(a)  # will print 1
print(b)  # will print 'B'
print(c)  # will print 3.0

A common use of variable unpacking is iterating over sequences of tuples of lists:

seq = [(1, 2, 3), (4, 5, 6), (7, 8, 9)]
for a, b, c in seq:
     printf(f'{a}, {b}, {c}')

Exchanging Variable Values

Tuple unpacking can be used to swap to variable values without using a third temporary variable.

v1 = 'A'
v2 = 'B'
v1, v2 = v2, v1
print(v1)  # will print B
print(v2)  # will print A

Plucking a Few Elements from the Beginning of a Tuple

t = (1, 2, 3, 4, 5)
a, b, *rest = values # a is 1, b is 2 and rest is (3, 4, 5)

If you want to discard the rest:

t = (1, 2, 3, 4, 5)
a, b, *_ = values

Slices

The same rule as for lists apply:

Slicing Lists and Tuples in Python

Named Tuples

Named tuples can be a simple alternative to objects.

Tuple Methods

count(val)

Counts the number of occurrences of the given value.