# Python Essentials Part 2

### Python Conditions

In Python, conditions are used to perform different actions based on whether a specific condition is true or false. Python uses conditional statements like `if`, `elif`, and `else` to control the flow of the program.

#### **if Statement**

The `if` statement is used to test a condition. If the condition evaluates to `True`, the block of code under the `if` statement is executed. If it's `False`, the block is skipped.

```python
x = 10
if x > 5:
    print("x is greater than 5")  # Output: x is greater than 5
```

#### 2\. **elif Statement**

The `elif` statement stands for "else if." It allows you to check multiple conditions sequentially. If the `if` condition is `False`, Python checks the next `elif` condition.

```python
x = 5
if x > 10:
    print("x is greater than 10")
elif x == 5:
    print("x is equal to 5")  # Output: x is equal to 5
```

#### 3\. **else Statement**

The `else` statement is used to execute a block of code if none of the previous `if` or `elif` conditions are `True`.

```python
x = 3
if x > 10:
    print("x is greater than 10")
elif x == 5:
    print("x is equal to 5")
else:
    print("x is less than 5")  # Output: x is less than 5
```

#### 4\. **Comparison Operators**

Conditions typically use comparison operators to evaluate the relationship between values:

* `==`: Equal to
    
* `!=`: Not equal to
    
* `>`: Greater than
    
* `<`: Less than
    
* `>=`: Greater than or equal to
    
* `<=`: Less than or equal to
    
    ```python
    x = 7
    if x == 7:
        print("x is equal to 7")  # Output: x is equal to 7
    ```
    
    #### 5\. **Logical Operators**
    
    You can use logical operators to combine multiple conditions:
    
    * `and`: Returns `True` if both conditions are true.
        
    * `or`: Returns `True` if at least one condition is true.
        

`not`: Returns `True` if the condition is false (negates the condition).

```python
x = 8
if x > 5 and x < 10:
    print("x is between 5 and 10")  # Output: x is between 5 and 10

if x == 8 or x == 10:
    print("x is either 8 or 10")  # Output: x is either 8 or 10

if not x == 5:
    print("x is not 5")  # Output: x is n
```

6\. **Nested Conditions**

You can nest one `if` statement inside another to create more complex condition checks.

```python
x = 10
y = 20
if x > 5:
    if y > 15:
        print("x is greater than 5 and y is greater than 15")  # Output: x is greater than 5 and y is greater than 15
```

### Python Loops

Loops in Python are used to repeatedly execute a block of code as long as a condition is true. Python primarily provides two types of loops: `for` loops and `while` loops.

#### 1\. `for` Loop

The `for` loop in Python is used to iterate over a sequence (such as a list, tuple, string, or range). It repeats the block of code for each element in the sequence.

```python
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)
```

#### 2\. `while` Loop

The `while` loop keeps executing as long as the condition is `True`. Once the condition becomes `False`, the loop stops.

```python
x = 1
while x <= 5:
    print(x)
    x += 1  # Increment x by 1
```

#### 3\. **Looping through a** `range()`

The `range()` function generates a sequence of numbers, which can be used with loops.

```python
for i in range(1, 6):
    print(i)
```

#### 4\. `break` Statement

The `break` statement is used to exit a loop prematurely, regardless of the loop's condition.

```python
for num in range(1, 10):
    if num == 5:
        break  # Exit the loop when num is 5
    print(num)
```

#### 5\. `continue` Statement

The `continue` statement skips the current iteration of the loop and moves to the next one.

```python
for num in range(1, 6):
    if num == 3:
        continue  # Skip the iteration when num is 3
    print(num)
```

#### 6\. `else` with Loops

Python allows using the `else` clause with loops. The `else` block is executed when the loop terminates naturally, meaning it did not terminate using `break`.

**Example with** `for` Loop:

```python
for num in range(1, 4):
    print(num)
else:
    print("Loop finished")
```

### Python User Input

In Python, you can prompt the user for input during the execution of a program using the built-in `input()` function. This allows interaction between the user and the program, enabling the user to provide data that the program can process.

#### **Getting User Input**

The `input()` function allows the user to type data at runtime. By default, the input is always returned as a string, so if numeric input is required, you’ll need to convert it.

```python
name = input("Enter your name: ")
print("Hello, " + name)
```

#### **Handling Numeric Input**

If the user is expected to input numbers, you must convert the string to the appropriate data type, such as `int` or `float`.

```python
age = input("Enter your age: ")  # Input is taken as a string
age = int(age)  # Convert the string to an integer
print(f"You are {age} years old.")
```

#### **Using** `input()` in Loops

You can combine the `input()` function with loops to repeatedly ask for user input.

```python
while True:
    name = input("Enter your name (type 'quit' to exit): ")
    if name == 'quit':
        break
    print(f"Hello, {name}!")
```

#### **Validation of User Input**

It’s a good idea to validate user input to ensure the program behaves correctly even if invalid data is entered.

**Example:**

```python
while True:
    age_input = input("Enter your age: ")
    if age_input.isdigit():  # Check if the input is a digit
        age = int(age_input)
        print(f"You are {age} years old.")
        break
    else:
        print("Invalid input. Please enter a number.")
```