Python Basics 7

Loops in Python, While Loop in Python, For Loop in Python...

Index

1. Loops in Python

2. While Loop in Python

3. For Loop in Python

4. Iterators and Iteration in Python

5. Break and Continue Keywords

6. range() Function

7. Linear Search

8. pass Statement

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1. Loops in Python

Definition:
Loops are a fundamental concept in programming that allow you to execute a block of code repeatedly, either a specific number of times or until a certain condition is met. This can save time, reduce code redundancy, and help in managing repetitive tasks effectively.

Use-Case Example:
Imagine you need to print numbers from 1 to 100. Instead of writing 100 print statements, you can use a loop to accomplish this task in just a few lines of code.

Syntax:

# Generic loop structure in Python
while condition:
    # Code block to be executed

for variable in sequence:
    # Code block to be executed

Rules:

• Loops can run indefinitely if not properly controlled.

• Loop conditions are evaluated before each iteration.

• Python supports while and for loops, each suited for different scenarios.

Basic Example:

# Printing numbers 1 to 5 using a while loop
i = 1
while i <= 5:
    print(i)
    i += 1

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2. While Loop in Python

Definition:
The while loop in Python repeatedly executes a block of code as long as the given condition is true. It's useful when the number of iterations is not known beforehand.

Use-Case Example:
A while loop can be used to keep a program running until a user decides to quit, such as in a menu-driven console application.

Syntax:

while condition:
    # Code block to be executed

Rules:

• The condition is checked before entering the loop. If the condition is False, the loop is skipped.

• The loop can become infinite if the condition never becomes False.

Basic Example:

# Counting down from 5 using a while loop
count = 5
while count > 0:
    print(count)
    count -= 1

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3. For Loop in Python

Definition:
The for loop in Python iterates over a sequence (like a list, tuple, or string) and executes a block of code for each item in the sequence.

Use-Case Example:
A for loop is ideal for iterating through a list of items, such as printing each element in a list of names.

Syntax:

for item in sequence:
    # Code block to be executed

Rules:

• The loop iterates over each item in the sequence.

• The loop ends when there are no more items to iterate over.

Basic Example:

# Printing each character in a string using a for loop
for char in "Python":
    print(char)

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4. Iterators and Iteration in Python

Definition:
An iterator is an object in Python that contains a countable number of values and can be traversed, i.e., iterated upon. The process of looping over an iterable object is called iteration.

Use-Case Example:
Iterators are useful when you need to traverse through all the elements of a collection, such as reading each line in a file.

Syntax:

iterable = [1, 2, 3]
iterator = iter(iterable)

for item in iterator:
    # Code block to be executed

Rules:

• Not all objects are iterable; they must implement the __iter__() and __next__() methods.

• Iteration stops when there are no more elements to retrieve.

Basic Example:

# Iterating through a list using an iterator
numbers = [1, 2, 3]
iterator = iter(numbers)
for num in iterator:
    print(num)

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5. Break and Continue Keywords

Definition:
The break and continue statements are control flow tools in loops. break exits the loop prematurely, while continueskips the rest of the code inside the loop for the current iteration and jumps to the next iteration.

Use-Case Example:

• break: Exiting a loop when a certain condition is met, such as stopping a search when an item is found.

• continue: Skipping even numbers while iterating through a list of numbers.

Syntax:

# break
for item in sequence:
    if condition:
        break

# continue
for item in sequence:
    if condition:
        continue

Rules:

• break ends the loop entirely.

• continue only skips the current iteration and continues with the next one.

Basic Example:

# Using break to exit loop
for num in range(10):
    if num == 5:
        break
    print(num)

# Using continue to skip even numbers
for num in range(10):
    if num % 2 == 0:
        continue
    print(num)

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6. range() Function

Definition:
The range() function in Python generates a sequence of numbers, often used with loops to iterate over a block of code a specified number of times.

Use-Case Example:
range() is commonly used in for loops to iterate a specific number of times or to create sequences of numbers.

Syntax:

range(start, stop[, step])

Rules:

• The start parameter is inclusive, and the stop parameter is exclusive.

• step is optional and defaults to 1.

Basic Example:

# Using range to print numbers from 0 to 4
for i in range(5):
    print(i)

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7. Linear Search

Definition:
Linear search is a simple search algorithm that checks each element in a list one by one until the desired element is found or the list ends.

Use-Case Example:
Linear search is useful when dealing with small or unsorted data sets where the overhead of more complex algorithms isn't justified.

Syntax:

def linear_search(sequence, target):
    for index, item in enumerate(sequence):
        if item == target:
            return index
    return -1

Rules:

• The time complexity is O(n), where n is the number of elements in the sequence.

Basic Example:

# Implementing linear search
def linear_search(sequence, target):
    for index, item in enumerate(sequence):
        if item == target:
            return index
    return -1

numbers = [10, 20, 30, 40, 50]
result = linear_search(numbers, 30)
print("Found at index:", result)

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8. pass Statement

Definition:
The pass statement in Python is a null operation. It is used as a placeholder for future code. When the pass statement is executed, nothing happens, but it can act as a placeholder in loops, functions, classes, or conditionals.

Use-Case Example:
pass is useful when you're working on new code and want to implement the logic later without causing syntax errors.

Syntax:

pass

Rules:

• The pass statement does nothing and is ignored by the interpreter.

• It is commonly used when a statement is syntactically required but you have nothing to write.

Basic Example:

# Using pass as a placeholder
for i in range(5):
    pass  # Placeholder for future implementation

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Python Basics by - Vishal Rajput