## What is variable ?

Variable is a label for a location in memory . Variable make us easy to understand as programmer.

Python has five standard data types −

- Numbers
- String
- List
- Tuple
- Dictionary

Let’s take a look on each of them.

## Number Data Type in Python

Python supports ** integers, floating point numbers and complex numbers.** They are defined as

`int`

, `float`

and `complex`

class in Python.```
# note variable is always at the left and we assign it with = to something like integer and float
# example we name our variable i for integer and f for float
i = 7
f = 3.5
# print the value of i and f to command prompt
print (i)
print (f)
# we can use type function to determine what is variable i and f is
print (type(i))
print (type(f))
## We can covert between the type to by using int and float function
print (float(i))
print (int(f))
```

Below are example of number type.

int | float | complex |
---|---|---|

10 | 0.0 | 3.14j |

100 | 15.20 | 45.j |

-786 | -21.9 | 9.322e-36j |

080 | 32.3+e18 | .876j |

-0490 | -90. | -.6545+0J |

-0x260 | -32.54e100 | 3e+26J |

0x69 | 70.2-E12 | 4.53e-7j |

Number System | Prefix |
---|---|

Binary | ‘0b’ or ‘0B’ |

Octal | ‘0o’ or ‘0O’ |

Hexadecimal | ‘0x’ or ‘0X’ |

Complex numbers are an extension of the familiar real number system in which all numbers are expressed as a sum of a real part and an imaginary part. Imaginary numbers are real multiples of the imaginary unit (the square root of -1), often written i in mathematics or j in engineering. Python has built-in support for complex numbers, which are written with this latter notation; the imaginary part is written with a j suffix, e.g., 3+1j. To get access to complex equivalents of the math module, use cmath. Use of complex numbers is a fairly advanced mathematical feature. If you’re not aware of a need for them, it’s almost certain you can safely ignore them.

Complex numbers are stored as a pair of machine-level double precision floating point numbers.

```
x = 3+1j
y = 3+2j
z = 3+3j
x = x + y + z
print (x)
print(type(x))
print(type(y))
print(type(z))
```

## Below are Operation that we can do with number type.

Operation | Meaning |
---|---|

`<` | strictly less than |

`<=` | less than or equal |

`>` | strictly greater than |

`>=` | greater than or equal |

`==` | equal |

`!=` | not equal |

`is` | object identity |

`is not` | negated object identity |

## Cheat Sheet For Number

Operation | Result | Notes | Full documentation |
---|---|---|---|

`x + y` | sum of x and y | ||

`x - y` | difference of x and y | ||

`x * y` | product of x and y | ||

`x / y` | quotient of x and y | ||

`x // y` | floored quotient of x and y | (1) | |

`x % y` | remainder of `x / y` | (2) | |

`-x` | x negated | ||

`+x` | x unchanged | ||

`abs(x)` | absolute value or magnitude of x | `abs()` | |

`int(x)` | x converted to integer | (3)(6) | `int()` |

`float(x)` | x converted to floating point | (4)(6) | `float()` |

`complex(re, im)` | a complex number with real part re, imaginary part im. im defaults to zero. | (6) | `complex()` |

`c.conjugate()` | conjugate of the complex number c | ||

`divmod(x, y)` | the pair `(x // y, x % y)` | (2) | `divmod()` |

`pow(x, y)` | x to the power y | (5) | `pow()` |

`x ** y` | x to the power y | (5) |

## String Data Type

Strings in Python are identified as a contiguous set of characters represented in the quotation marks. Python allows either pair of single or double quotes. Subsets of strings can be taken using the slice operator ([ ] and [:] ) with indexes starting at 0 in the beginning of the string and working their way from -1 to the end.

The plus (+) sign is the string concatenation operator and the asterisk (*) is the repetition operator. For example −

```
#### Declare Variable str and assign string to it
str = "Welcome to Python String Tutorial"
print (len(str)) # Prints length of the str
print (str) # Prints complete string
print (str[0]) # Prints first character of the string
print (str[2:5]) # Prints characters starting from 3rd to 5th
print (str[2:]) # Prints string starting from 3rd character
print (str * 2) # Prints string two times
print (str + " More Text") # Prints concatenated string
print (str.lower()) # Prints to lower
print (str.upper()) # Prints all to upper
```

## List data type in Python

```
list1 = [ 'Apple' , 'Banana' , "Stawberry" ] ## Declare 3 List Element
list1[0] = "Change from apple to Chili" ## Remember to access List 0 is the first element
list2 = ['Name' , 'Fruit' , '123']
## looping list
for x in list1:
print (x)
print (list1) # Prints complete list
print (list1[0]) # Prints first element of the list
print (list1[1:3]) # Prints elements starting from 2nd till 3rd
print (list1[2:]) # Prints elements starting from 3rd element
print (list1 * 2) # Prints list two times
print (list1 + list2) # Prints concatenated lists
print (len(list1)) ### print how many element in list which is 3
list1.append ("New Element") ### append to list1
list1.insert (1, 'New Item') ### insert in list[1] New Item
del list1[0] ### remove item from list[0]
```

## Tuple Data Type in Python

While list we begin to declare it with [] , tuple we declare it with () . Unlike List , List can be change while Tuple can’t be change . It is like read only data . Let’s take a look from example below.

```
tuple1 = ('12345' , 'Some Text Here' , 'Final text here 12345') ## declare tuple Notice we use ()
tuple2 = ('54321', "another text here")
print (len(tuple1)) ## print tuple1 length
print (len(tuple2)) ## print tuple2 length
print (tuple1) # Prints complete tuple
print (tuple1[0]) # Prints first element of the tuple
print (tuple1[1:3]) # Prints elements starting from 2nd till 3rd
print (tuple1[2:]) # Prints elements starting from 3rd element
print (tuple2 + tuple1) # prints tuple 2 and follow by tuple 1
#### We try to edit tuple1 with result of error
tuple1[0] = 'Error' # TypeError: 'tuple' object does not support item assignment
```

## Dictionary Data Type in Python

**Dictionary **in Python is an unordered collection of data values, used to store data values like a map, which unlike other Data Types that hold only single value as an element, Dictionary holds ** key:value** pair. Key value is provided in the dictionary to make it more optimized. Each key-value pair in a Dictionary is separated by a colon

**:**, whereas each key is separated by a ‘comma’.

A Dictionary in Python works similar to the Dictionary in a real world. Keys of a Dictionary must be unique and of *immutable *data type such as Strings, Integers and tuples, but the key-values can be repeated and be of any type.

```
dict1 = {
'key1' : 'value1',
'key2' : 'value2',
'key3' : 'value3',
### Nested Dictionary
'key4' : { 'A' : 'Welcome' , 'B' : 'To' , 'C' : 'Python'}
}
##### Let's see what we can do with Dictionary
print (dict1) ## print key and value of dict1
print (dict1.get('key1')) ## print key1 value which is value1
dict1 ['key1'] = 'somevalue' ## change key1 value to somevalue
dict1 ["key5"] = 'somevalue5' ## Adding an item to the dictionary is done by using a new index key and assigning a value to it:
del dict1["key2"] ## remove key2 from dictionary
dict2 = dict1.copy() ## Copy Dictionary
#### We can loop over the key .
for x in dict1: ## Print all key names in the dictionary, one by one:
print(x)
#### Print all values in the dictionary, one by one:
for x in dict1:
print(dict1[x])
#### You can also use the values() function to return values of a dictionary:
for x in dict1.values():
print(x)
#### Loop through both keys and values, by using the items() function:
for x, y in dict1.items():
print(x, y)
```

Source : https://docs.python.org/3/library/stdtypes.html https://python-reference.readthedocs.io/en/latest/docs/complex/ https://www.geeksforgeeks.org/python-dictionary/ https://www.w3schools.com/python/python_dictionaries.asp https://www.tutorialspoint.com/python3/python_variable_types.htm |