Collections

 Collections

In Python, the collections module is part of the standard library and provides specialized container datatypes that extend the functionality of built-in containers like dict, list, set, and tuple. Below are the main classes and their use cases:

There are four collection data types in the Python programming language:

• List is a collection which is ordered and changeable. Allows duplicate members.
• Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
• Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
• Dictionary is a collection which is ordered** and changeable. No duplicate members.

Mutable : In programming, mutable refers to an object or data type that can be modified or changed after it is created. Eg. Array, list

Immutable : when an object or data type that can't be modified or changed after it is created is called immutable. int, float, char

• Lists: Lists are used to store multiple items in a single variable.

• List can contain duplicate items.

• List in Python are Mutable. Hence, we can modify, replace or delete the items.

• List are ordered. It maintain the order of elements based on how they are added.

• Accessing items in List can be done directly using their position (index), starting from 0.

·        You can create a list using square brackets [] or the list() constructor.

fruits = ["apple", "banana", "cherry"]

# Using square brackets

my_list = [1, 2, 3, 4, 5]

---

# Using list()

another_list = list(("Palak", "Methi", "Tomato"))  

# Notice the double parentheses

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# Lists can contain different data types

mixed_list = [1, "hello", 3.14, True]

More details on List 

• Tuples: A tuple is a collection which is ordered and immutable and allow duplicate values.
• Tuples are used to store multiple items in a single variable.
• Tuples are written with round brackets.

coordinates = (10, 20)

thistuple = ("apple", "banana", "cherry")
print(thistuple)

More details on Tuple

• Sets: A set is a collection which is unordered,unique collection, unchangeable*, and unindexed. 

• Sets are used to store multiple items in a single variable.

  Set is one of 4 built-in data types in Python used to store collections of data, the other 3 are List, Tuple, and Dictionary, all with different qualities and usage.

unique_numbers = {1, 2, 3}

---

 thisset = {"apple", "banana", "cherry"}

print(thisset)

More details on Set

• Dictionaries: Key-value pairs.

• Dictionaries are used to store data values in key:value pairs.

• A dictionary is a collection which is ordered*, changeable and do not allow duplicates.

• Dictionaries are written with curly brackets, and have keys and values:

student = {"name": "John", "age": 20}

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

More details on Dict

Counter

• Purpose: Counts the occurrences of elements in an iterable.
• Usage:

from collections import Counter

 

data = ['a', 'b', 'c', 'a', 'b', 'b']

counter = Counter(data)

print(counter)  # Output: Counter({'b': 3, 'a': 2, 'c': 1})

print(counter.most_common(1))  # Output: [('b', 3)] 

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6. Input and Output

• Input: Get data from the user.

name = input("Enter your name: ")

• Output: Print data to the console.

print(f"Hello, {name}!")

More Details on Input Output

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7. Comments

• Used for documentation and are ignored by the interpreter.

# This is a single-line comment.

"""

This is a multi-line comment.

Useful for longer explanations.

"""

---

8. Error Handling

• Manage errors using try-except blocks.

try:

    result = 10 / 0

except ZeroDivisionError:

    print("Cannot divide by zero.")

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9. Modules and Libraries

• Python includes a rich set of libraries for various tasks.

import math

print(math.sqrt(16))

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10. File Handling

• Reading and writing files.

with open("example.txt", "w") as file:

    file.write("Hello, Python!")

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Example: Combining Building Blocks

# Program to calculate the factorial of a number

def factorial(n):

    if n == 0 or n == 1:

        return 1

    else:

        return n * factorial(n - 1)

try:

    num = int(input("Enter a number: "))

    if num < 0:

        print("Factorial is not defined for negative numbers.")

    else:

        print(f"The factorial of {num} is {factorial(num)}")

except ValueError:

    print("Please enter a valid number.")

These building blocks provide the foundation for creating complex and powerful Python applications.

Keywords : Keywords in Python are reserved words that have predefined meanings and purposes. They cannot be used as variable names, function names, or identifiers. Python keywords are case-sensitive and written in lowercase, except for True, False, and None.
 

List of Python Keywords

Here is the list of all keywords in Python 3:

True	Boolean value, the opposite of False.
and	Logical AND operator.
as	Used for aliasing imports.
assert	For debugging; tests a condition.
async	Defines asynchronous functions.
await	Waits for the result of an async call.
break	Exits a loop prematurely.
class	Defines a class.
continue	Skips the rest of the loop iteration.
def	Defines a function.
del	Deletes an object.
elif	Else if condition in control structures.
else	Defines the alternative block.
except	Handles exceptions.
finally	Executes code after try-except.
for	Loop construct.
from	Used in imports.
global	Declares a global variable.
if	Conditional statement.
import	Imports modules.
in	Membership operator or loop construct.
is	Tests object identity.
lambda	Defines an anonymous function.
nonlocal	Declares a non-local variable.
not	Logical NOT operator.
or	Logical OR operator.
pass	Acts as a placeholder.
raise	Raises an exception.
return	Returns a value from a function.
try	Defines a block to test for errors.
while	Loop construct.
with	Simplifies exception handling.
yield	Pauses and resumes a generator function.

Key Points

1.    Keywords cannot be used as identifiers.

2.    They are essential for defining the structure and behavior of Python programs.

Python's simplicity ensures that the keyword set is small and meaningful.