# Variables and Data Types

### What's Variable 

Variables are containers for storing data values.

Python has no command for declaring a variable.

A variable is created the moment you first assign a value to it.

Variables do not need to be declared with any particular *type*, and can even change type after they have been set.

**Types are only associated with objects of variables**

### Variable Types

**Strings**

```
# define variable
name = "Ayman"
print(name)        
Output: Ayman
```

```
# new line
name = "Ayman\nAyman" 
print(name)        
Output: Ayman
          Ayman
```

```
# print \n in output -raw string-
name = r'Ayman\nAyman'  
print(name)        
Output: Ayman\nAyman
```

```
# unicode string
name = u'Ayman'
# convert unicode to string  
str(name)
# convert string to unicode
unicode(name) 
```

```
# add formating
name="""
Ayman
        Ayman
"""
print(name)
Output:
Ayman
	Ayman
```

#### Numbers

```
x = 1    # int
y = 2.8  # float
z = 1j   # complex
```

### Operation on Variables

#### String Operations

* Strings are immutable 
* Concatenation\
  `var1 + var2 = 'var1var2'`\
  `var1 + '' +var2 = 'var1 var2'`
* Repeated sequence\
  `buffer = "A"*100`
* Slicing \
  `string[start:end:step]`
* int to string\
  `int("100")`\
  `Output: 100`
* string.find(*value*)
* string.replace(*old\_value, new\_value*)
* and a lot more ... check [manual](https://docs.python.org/3/library/stdtypes.html)

#### Numbers Operations

normal as other languages

`x**y (x power y)`

### String Formatting

#### Option #1: %-formatting

```
name = "Ayman"
age = 22
print("Hello, %s." % name)
Output: 'Hello, Ayman.'
print("Hello, %s. You are %s." % (name, age))
Output: 'Hello Ayman. You are 22.'
```

#### Option #2: str.format()

```
name = "Ayman"
age = 22
print("Hello, {}. You are {}.".format(name, age))
Output: 'Hello, Ayman. You are 22.'
print("Hello, {1}. You are {0}.".format(age, name))
Output: 'Hello, Ayman. You are 22.'
```

### Memory Location

```
x = 10
id(x)                  # Output: 9789280
hex(id(x))             # Output: '0x955f60'
name.__repr__          # Output: <method-wrapper '__repr__' of int object at 0x955f60>

```

### Casting

If you want to specify the data type of a variable, this can be done with casting.

```
x = str(10)    # x will be '10'
y = int(10)    # y will be 10
z = float(10)  # z will be 10.0
```

### Get the Type

You can get the data type of a variable with the `type()` function.

```
x = 10
y = "Ayman"        
print(type(x))        # <class 'int'>
print(type(y))        # <class 'str'>
```

### Single and Double Quotes

both are the same

### Case-Sensitive

Variable names are case-sensitive.


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