Programming Python

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Scripting Language Lab3

Arrays

Arrays in Python are not like arrays in Java or C but are more similar to lists.
An array is a data structure that stores values of the same type.
This is the main difference between arrays and lists in Python.
To use arrays in Python, you need to import the array module from Python’s standard libraries because arrays are not considered primitive data types like integers or strings.

from array import *


Below is an example of an array declaration:

```Python
array_name = array(data_type_code, [initial_values])
Data Type Code Description
b Represents a signed integer of size 1 byte
B Represents an unsigned integer of size 1 byte
c Represents a character of size 1 byte
u Represents a Unicode character of size 2 bytes
h Represents a signed integer of size 2 bytes
H Represents an unsigned integer of size 2 bytes
i Represents a signed integer of size 2 bytes
I Represents an unsigned integer of size 2 bytes
w Represents a Unicode character of size 4 bytes
l Represents a signed integer of size 4 bytes
L Represents an unsigned integer of size 4 bytes
f Represents a floating-point number of size 4 bytes
d Represents a floating-point number of size 8 bytes

Individual elements can be accessed using their index, and arrays are indexed starting from 0.

from builtins import print

my_array = array('i', [1, 2, 3, 4, 5])
print(my_array[1])
print(my_array[2])
print(my_array[0])
print()

my_array = array('i', [1, 2, 3, 4, 5])
for i in my_array:
    print(i)

Adding Elements to an Array

Adding an element to an array using the append method:

my_array = array('i', [1, 2, 3, 4, 5])
my_array.append(6)

Adding an element to a specific index using the insert method:

my_array.insert(0, 0)

The inserted value is placed in the appropriate position in the array, shifting the remaining elements by one index.

Extending an Array

In Python, you can extend an array with more than one value using the extend method:

my_array = array('i', [1, 2, 3, 4, 5])
my_extend_array = array("i", [6, 7, 8, 9, 10])
my_array.extend(my_extend_array)
print(my_array)

You can also add elements from a list to an array using the fromlist method:

my_array = array('i', [1, 2, 3, 4, 5])
c = [11, 12, 13]
my_array.fromlist(c)

Removing Elements from an Array

Removing an element from an array using the remove method:

my_array = array('i', [1, 2, 3, 4, 5])
my_array.remove(4)

Removing the last element from an array using the pop method:

my_array = array('i', [1, 2, 3, 4, 5])
my_array.pop()

Finding Elements in an Array

Using the index method to find the first occurrence of a value:

my_array = array('i', [1, 2, 3, 4, 5])
print(my_array.index(5))

my_array = array('i', [1, 2, 3, 3, 5])
print(my_array.index(3))

Reversing an Array

Using the reverse method:

my_array = array('i', [1, 2, 3, 4, 5])
my_array.reverse()
print(my_array)

Getting Array Information

Finding the memory address and length of an array:

my_array = array('i', [1, 2, 3, 4, 5])
print(my_array.buffer_info())

Counting the occurrences of a specific value:

my_array = array('i', [1, 2, 3, 3, 5])
print(my_array.count(3))

Converting an Array

Converting an array to a string:

my_array1 = array('u', ['s', 'p', 'a', 'm'])
print(my_array1)
print(my_array1.tounicode())

Converting an array to a list:

my_array = array('i', [1, 2, 3, 4])
list_version = my_array.tolist()

Dictionaries

Dictionaries are data structures used to map arbitrary keys to values.
They can be indexed similarly to lists using square brackets containing the key.

ages = {"I": 78, "You": 20, "Him": 24}
print(ages["I"])
print(ages["Him"])

Each dictionary element is represented as a key: value pair.
If a non-existent key is accessed, it raises a KeyError.

colors = {
    "red": [255, 0, 0],
    "green": [0, 255, 0],
    "blue": [0, 0, 255]
}
print(colors["red"])
print(colors["yellow"])  # KeyError

Only immutable objects can be used as dictionary keys. Lists and arrays cannot be used as keys.

bad_dict = {[1, 2, 3]: "one two three"}  # TypeError

Dictionary Methods

Checking if a key exists in a dictionary using in and not in:

nums = {1: "one", 2: "two", 3: "three"}
print(1 in nums)
print("three" in nums)
print(4 not in nums)

Getting values using the get method:

pairs = {
    "orange": [2, 3, 40], 0: "spam", True: False, None: "True", 2: "apple"
}
print(pairs.get("orange"))
print(pairs.get(7))
print(pairs.get(1235, "not in dictionary"))
print(len(pairs))

Merging dictionaries:

fish = {'name': "Nemo", 'hands': "fins", 'special': "gills"}
dog = {'name': "Clifford", 'hands': "paws", 'color': "red"}
# Python 3.5+
fishdog = {**fish, **dog}
print(fishdog)

Slicing Lists

Extracting specific portions of a list:

squares = [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
print(squares[2:6])
print(squares[:7])
print(squares[::2])

Useful String Methods

print(",".join(["spam", "eggs", "spam"]))
print("Hello Me".replace("Me", "world"))
print("This is a sentence.".upper())
print("Numbers: {0} {1} {2}".format(4, 5, 6))

Tasks to Complete

2-6 must be added to GitHub.

Python