Types and Type Conversions

Reminder

First let us recall which data types exist in Python. The list below contains the data types available in Python along with examples. Please study them carefully so this topic is easier to understand.

Note: I will not write Turkish equivalents of Python-related terms — learning the English terms is more useful.

• Numbers
  • int()
    • variable = 1
  • float()
    • variable = 0.1
    • variable = 0.00012
• String
  • str()
    • variable = "string"
    • variable = 'string'
    • variable = """long string"""
    • variable = '''long string'''
• List
  • list()
    • variable = [1, 2, 3, 4]
    • variable = ["1", "2", "3", "4"]
    • variable = [1.1, 2.2, 3.3, 4.4]
    • variable = [{1: 2}, {2: 3}, {3: 4}]
• Tuple
  • variable = 1, 2, 3, 4
  • variable = (1, 2, 3, 4)
  • variable = "1", "2", "3", "4"
• Dictionary
  • dict()
    • variable = {1: 2, "a": "b", "c": 2}
    • variable = dict(a=1, b=2, c=3)
    • variable = {1: [3, 4], "a": "b", "c": 2}

Type Conversions in Python

Now that we have a good reminder, let us get to the main topic. These operations are really quite simple. Here is the short version:

You have a variable with a value whose type you know (or can find using type()). You then call the type function/method for the type you want to convert to.

In a previous article on the input() function, we saw that every value received via input() (from the user) arrives as a string.

This is where the problem starts: if I ask the user to enter a number and they type 2049, it does not reach my variable as a number — it arrives as a string, and I need to check and convert it.

string_data = input("Please enter any number you want >> ")
print(type(string_data))
print(string_data / 1)   # dividing by 1 — will raise an error if it is not a number

The error we get will be TypeError — we tried to divide a string by an integer.

<class 'str'>
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'str' and 'int'

We need to convert the incoming value to int or float:

string_data = input("Please enter any number you want >> ")
string_data = int(string_data) / 1
print(type(string_data))
print(string_data)

Result:

<class 'int'>
2049

No error this time. Now let us look at the other conversion functions.

int()

int() argument must be a string, a bytes-like object or a number

Converts the given object to int if possible.

>>> int("10")
10
>>> int(0.21)
0

Note: int("10.1") — a string in float format cannot be converted directly to int; you need to convert it to float first.

float()

float() argument must be a string or a number

Converts the given object to float if possible.

>>> float("10")
10.0
>>> float("10.1")
10.1
>>> float(0.21)
0.21

str()

Converts any object to string.

>>> str(10)
'10'
>>> str(10.1)
'10.1'
>>> str(False)
'False'
>>> str(int)
"<class 'int'>"
>>> str({1: 2})
'{1: 2}'
>>> str([1, 2])
'[1, 2]'

complex()

first argument must be a string or a number

Takes one or two parameters. If only one parameter is given it can be a string or a number; if two parameters are given the first cannot be a string. The second parameter is the imaginary part.

>>> complex(10)
(10+0j)
>>> complex("10")
(10+0j)
>>> complex(1, 2)
(1+2j)
>>> complex(3.4, 4)
(3.4+4j)

dict()

Creates a dict from the parameter names and values.

>>> dict(a=1)
{'a': 1}
>>> dict(name="hakan", no=0.538)
{'name': 'hakan', 'no': 0.538}

list()

Converts a tuple or string to a list.

>>> list("test")
['t', 'e', 's', 't']
>>> list((1, 2))
[1, 2]