# How to declare a variable in Python

In Python, you can declare a variable by assigning a value to it using the equals sign (=) operator. Here is the basic syntax for declaring a variable:

```variable_name = value
```

Here, `variable_name` is the name of the variable, and `value` is the value that you want to assign to the variable.

For example, to declare a variable named `x` with the value of `10`, you can write:

```x = 10
```

You can also declare multiple variables in a single line by separating them with commas. For example:

```a = 1
b = 2
c, d = 3, 4
```

In the above example, `a` is assigned the value `1`, `b` is assigned the value `2`, `c` is assigned the value `3`, and `d` is assigned the value `4`.

### Numbers:

In Python, there are three types of numbers: integers, floating-point numbers, and complex numbers.

1. Integers: Integers are whole numbers with no decimal point. In Python, integers are represented by the `int` data type. For example:
```x = 10
y = -5
```
1. Floating-point numbers: Floating-point numbers, also called “floats”, are numbers with a decimal point. In Python, floating-point numbers are represented by the `float` data type. For example:
```a = 3.14
b = -0.5
```
1. Complex numbers: Complex numbers are numbers with both a real part and an imaginary part. In Python, complex numbers are represented by the `complex` data type. You can create a complex number by specifying the real part and the imaginary part, separated by a `+` or `-` sign. For example:
```z1 = 2 + 3j
z2 = 4 - 2j
```

In Python, you can perform mathematical operations on numbers using arithmetic operators such as `+`, `-`, `*`, `/`, `%`, and `**` (for exponentiation). For example:

```x = 10
y = 3
z = x + y    # z will be 13
w = x ** 2   # w will be 100 (10 squared)
```

It’s important to keep in mind that floating-point numbers are not exact, so you may encounter rounding errors when performing certain calculations.

### Strings:

In Python, a string is a sequence of characters, enclosed in either single quotes (‘…’) or double quotes (“…”). Here’s an example of how to create a string variable:

```message = "Hello, world!"
```

In the above example, `message` is a variable containing a string value.

You can perform a wide range of operations on strings in Python. Here are a few examples:

1. Concatenation: You can concatenate (join) two or more strings together using the `+` operator. For example:
```greeting = "Hello"
name = "Alice"
message = greeting + " " + name
```

In the above example, `message` will be the string “Hello Alice”.

1. String formatting: You can insert values into a string using placeholders (marked with curly braces) and the `format` method. For example:
```name = "Bob"
age = 30
message = "My name is {} and I'm {} years old".format(name, age)
```

In the above example, `message` will be the string “My name is Bob and I’m 30 years old”.

1. Substring: You can extract a substring (a portion of a string) using slicing. For example:
```message = "Hello, world!"
substring = message[0:5]   # Gets the first five characters of the string
```

In the above example, `substring` will be the string “Hello”.

There are many other operations you can perform on strings in Python, including searching for substrings, replacing parts of a string, converting case, and more.

### Multiple Assignments:

In Python, you can assign values to multiple variables in a single line using the multiple assignment syntax. The syntax for multiple assignment looks like this:

```variable1, variable2, variable3 = value1, value2, value3
```

Here, `variable1`, `variable2`, and `variable3` are the names of the variables you want to assign values to, and `value1`, `value2`, and `value3` are the values you want to assign to those variables.

For example, you can assign values to three variables `x`, `y`, and `z` in a single line like this:

```x, y, z = 10, 20, 30
```

In the above example, `x` will be assigned the value `10`, `y` will be assigned the value `20`, and `z` will be assigned the value `30`.

You can also use multiple assignment to swap the values of two variables. For example:

```x, y = y, x
```

In the above example, the values of `x` and `y` are swapped, so the value of `x` is now what `y` used to be, and vice versa.

Multiple assignment is a convenient way to assign values to multiple variables at once and can make your code more concise and readable.