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Tuples

S.Madhumalar

Assistant Professor

C.P.A College, Bodinayakanur

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Tuples

  • Tuples are very similar to lists, but they are immutable (i.e., unchangeable)

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  • Tuples are written with round brackets as follows:

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t1 = (1, 2, 3)

t2 = (“a”, “b”, “c”, ”d”)

t3 = (200, “A”, [4, 5], 3.2)

print(t1)

print(t2)

print(t3)

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Tuples

  • Like lists, tuples can:
    • Contain any and different types of elements
    • Contain duplicate elements (e.g., (1, 1, 2))
    • Be indexed exactly in the same way (i.e., using the [] brackets)
    • Be sliced exactly in the same way (i.e., using the [::] notation)
    • Be concatenated (e.g., t = (1, 2, 3) + (“a”, “b”, “c”))
    • Be repeated (e.g., t = (“a”, “b”) * 10)
    • Be nested (e.g., t = ((1, 2), (3, 4), ((“a”, “b”, ”c”), 3.4))
    • Be passed to a function, but will result in pass-by-value and not pass-by-reference outcome since it is immutable
    • Be iterated over

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Examples

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t1 = ("a", "b", "c")

print(t1[::-1])

t2 = ("a", "b", "c")

t3 = t1 + t2

print(t3)

t3 = t3 * 4

print(t3)

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for i in t3:

print(i, end = " ")

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print()

This will print the elements of t1 in

a reversed order, but will not change

t1 itself since it is immutable

This will concatenate t1 and t2 and �assign the result to t3 (again, t1 and�t2 will be unchanged since they are �immutable)

This will repeat t3 four times and �assign the result to t3. Hence,

t3 will be overwritten (i.e., NOT �changed in place- because it is immutable-, but redefined with a new value)

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Examples

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t4 = ((1, 2, 3), ("a", "b", "c"))

for j in t4:

for k in j:

print(k,end = " ")

print()

This is an example of nesting, where �a matrix with 2 rows and�3 columns is created. The first row �includes the elements 1, 2, and 3. �The second row includes the elements �“a”, “b”, and “c”.

This outer loop iterates over each element in t4; that is, it gets first the element (1, 2, 3) and second the element (“a”, “b”, “c”)

This inner loop iterates over each element read by the outer loop; that is, it first iterates over the elements of the element (1, 2, 3), and second it iterates over the elements of the element (“a”, “b”, “c”)

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Examples

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def func1(t):

t = t * 2

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t = (1, 2, 3)

print(t)

func1(t)

print(t)

This will output (1, 2, 3)

This will also output (1, 2, 3) since tuples are immutable, hence, will always exhibit a passed-by-value behavior

This change on t remains local to the function�since a value of t was passed and not a �reference to it

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Using Functions with Tuples

  • You can also use functions with tuples

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t1 = (1, 2, 3, 1, 5, 1)

print(t1.count(1))

print(t1.index(1))

The count(x) function returns the number of �elements with the specified value x (e.g., x is 1 �in this example)

The index(x) function returns the index of the first element with the specified value x (e.g., x is 1 in this example)

Output:

3

0

In fact, Python has only these two built-in functions that can be used on tuples

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Towards Dictionaries

  • Lists and tuples hold elements with only integer indices

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  • So in essence, each element has an index (or a key) which can only be an integer, and a value which can be of any type (e.g., in the above list/tuple, the first element has key 0 and value 45)
    • What if we want to store elements with non-integer indices (or keys)?

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45

“Coding”

4.5

7

89

0

1

2

3

4

Integer �Indices

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Dictionaries

  • In Python, you can use a dictionary to store elements with keys of any types (not necessarily only integers like lists and tuples) and values of any types as well

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  • The above dictionary can be defined in Python as follows:

dic = {"NUM":45, 1000:"coding", 2000:4.5, 3.4:7, "XXX":89}

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45

“Coding”

4.5

7

89

“NUM”

1000

2000

3.4

“XXX”

keys of different types

Each element is a key:value pair, and elements are separated by commas

key

value

Values of different types

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Dictionaries

  • In summary, dictionaries:
    • Can contain any and different types of elements (i.e., keys and values)
    • Can contain only unique keys but duplicate values

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    • Can be indexed but only through keys (i.e., dic2[“a”] will return 1 but dic2[0] will return an error since there is no element with key 0 in dic2 above)

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Output: {'a': 2, 'b': 2}

dic2 = {"a":1, "a":2, "b":2}

print(dic2)

The element “a”:2 will override the element “a”:1

because only ONE element can have key “a”

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Dictionaries

  • In summary, dictionaries:
    • CANNOT be concatenated
    • CANNOT be repeated
    • Can be nested (e.g., d = {"first":{1:1}, "second":{2:"a"}}
    • Can be passed to a function and will result in a pass-by-reference and not pass-by-value behavior since it is immutable (like lists)

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Output:

{'first': {1: 1}, 'second': {2: 'a'}}

{'first': [1, 2, 3], 'second': {2: 'a'}}

def func1(d):

d["first"] = [1, 2, 3]

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dic = {"first":{1:1}, "second":{2:"a"}}

print(dic)

func1(dic)

print(dic)

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Dictionaries

  • In summary, dictionaries:
    • Can be iterated over

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Output:

dic = {"first": 1, "second": 2, "third": 3}

for i in dic:

print(i)

How to get the values?

first

second

third

ONLY the keys will be returned.

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Dictionaries

  • In summary, dictionaries:
    • Can be iterated over

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Output:

dic = {"first": 1, "second": 2, "third": 3}

for i in dic:

print(dic[i])

1

2

3

Values can be accessed via indexing!

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Adding Elements to a Dictionary

  • How to add elements to a dictionary?
    • By indexing the dictionary via a key and assigning a corresponding value

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Output:

dic = {"first": 1, "second": 2, "third": 3}

print(dic)

dic["fourth"] = 4

print(dic)

{'first': 1, 'second': 2, 'third': 3}

{'first': 1, 'second': 2, 'third': 3, 'fourth': 4}

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Adding Elements to a Dictionary

  • How to add elements to a dictionary?
    • By indexing the dictionary via a key and assigning a corresponding value

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Output:

dic = {"first": 1, "second": 2, "third": 3}

print(dic)

dic[”second"] = 4

print(dic)

{'first': 1, 'second': 2, 'third': 3}

{'first': 1, 'second’: 4, 'third': 3}

If the key already exists, �the value will be overridden

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Deleting Elements to a Dictionary

  • How to delete elements in a dictionary?
    • By using del

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Output:

dic = {"first": 1, "second": 2, "third": 3}

print(dic)

dic["fourth"] = 4

print(dic)

del dic["first"]

print(dic)

{'first': 1, 'second': 2, 'third': 3}

{'first': 1, 'second': 2, 'third': 3, 'fourth': 4}

{'second': 2, 'third': 3, 'fourth': 4}

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Deleting Elements to a Dictionary

  • How to delete elements in a dictionary?
    • Or by using the function pop(key)

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Output:

dic = {"first": 1, "second": 2, "third": 3}

print(dic)

dic["fourth"] = 4

print(dic)

dic.pop(“first”)

print(dic)

{'first': 1, 'second': 2, 'third': 3}

{'first': 1, 'second': 2, 'third': 3, 'fourth': 4}

{'second': 2, 'third': 3, 'fourth': 4}

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Dictionary Functions

  • Many other functions can also be used with dictionaries

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Function

Description

dic.clear()

Removes all the elements from dictionary dic

dic.copy()

Returns a copy of dictionary dic

dic.items()

Returns a list containing a tuple for each key-value pair in dictionary dic

dic.get(k)

Returns the value of the specified key k from dictionary dic

dic.keys()

Returns a list containing all the keys of dictionary dic

dic.pop(k)

Removes the element with the specified key k from dictionary dic

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Dictionary Functions

  • Many other functions can also be used with dictionaries

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Function

Description

dic.popitem()

Removes the last inserted key-value pair in dictionary dic

dic.values()

Returns a list of all the values in dictionary dic