📘 PAPER 2: OBJECT ORIENTED PROGRAMMING WITH PYTHON UNIT 4 – Dictionaries, Functions, File Handling & Regular Expressions (university of allahabad)

 

🔴 UNIT 4 – Dictionaries, Functions, File Handling & Regular Expressions

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1️⃣ Dictionaries in Python

✅ Definition

A dictionary is an unordered collection of data stored as key–value pairs.

Example:

student = {
    "name": "Amit",
    "age": 20,
    "course": "MCA"
}

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🔹 Characteristics

✔ Key-value based
✔ Mutable
✔ Keys must be unique
✔ Fast access

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🔹 Accessing Dictionary Elements

print(student["name"])

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🔹 Adding & Updating Values

student["age"] = 21
student["city"] = "Delhi"

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🔹 Deleting Elements

del student["age"]

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2️⃣ Counting Frequency Using Dictionary

Example:

text = "banana"
freq = {}

for ch in text:
    if ch in freq:
        freq[ch] += 1
    else:
        freq[ch] = 1

print(freq)

Output:

{'b':1, 'a':3, 'n':2}

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3️⃣ Python Functions

✅ Definition

A function is a block of reusable code.

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🔹 Function Syntax

def function_name(parameters):
    statements
    return value

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🔹 Types of Arguments

1. Positional

2. Keyword

3. Default

4. Variable-length

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Example:

def add(a, b=5):
    return a + b

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4️⃣ Passing Function as Argument

def square(x):
    return x*x

def fun(f, value):
    return f(value)

print(fun(square, 5))

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5️⃣ Lambda Function

Definition:

Anonymous function written in one line.

square = lambda x: x*x
print(square(5))

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6️⃣ Map Function

nums = [1,2,3]
result = list(map(lambda x: x*2, nums))

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7️⃣ List Comprehension

squares = [x*x for x in range(5)]

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8️⃣ File Handling in Python

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🔹 Opening a File

f = open("data.txt", "r")

File Modes:

Mode	Meaning
r	Read
w	Write
a	Append
r+	Read + Write

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🔹 Reading File

f.read()

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🔹 Writing File

f.write("Hello Python")

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🔹 Closing File

f.close()

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9️⃣ String Processing

Common String Functions:

s.upper()
s.lower()
s.replace()
s.split()
s.strip()

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🔟 Regular Expressions (RegEx)

Definition:

Regular expressions are used for pattern matching.

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Common Symbols

Symbol	Meaning
.	Any character
^	Start of string
$	End of string
*	Zero or more
+	One or more
[a-z]	Range

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Example:

import re
pattern = re.search("python", "I love python")