Type Casting in Python

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Type Casting is the process of converting a value of one data type to another.  Used to convert user input from string to integer, rounding a float to an integer, changing an integer to a string, and so on. If we create a variable for the four main data types, we can print what each of the data types is:

name = ("Bob")   # <-- STRING
age = 16         # <-- INTEGER
distance = 4.5   # <-- FLOAT
student = True   # <-- BOOLEAN

print(type(name))
print(type(age))
print(type(distance))
print(type(student))

Outputs:

<class 'str'>
<class 'int'>
<class 'float'>
<class 'bool'>

To convert ‘age’ to a ‘float’:

name = ("Bob")   # <-- STRING
age = 16         # <-- INTEGER
distance = 4.5   # <-- FLOAT
student = True   # <-- BOOLEAN

age = float(age)
print(age)

Outputs ‘age’ with a decimal having converted it to a float:

16.0

To convert a ‘float’ to an ‘integer’, the decimal portion will be cut off (truncated).

name = ("Bob")   # <-- STRING
age = 16         # <-- INTEGER
distance = 4.5   # <-- FLOAT
student = True   # <-- BOOLEAN

distance = int(distance)
print(distance)
print(type(distance))

Output:

4
<class 'int'>

Converting a ‘float’ or an ‘integer’ to a ‘Boolean’ will set it to True for ALL values other than zero.  Converting a ‘string’ to a ‘Boolean’ will be always be True unless the value is blank.  This can be useful to validate all fields in a form have been filled and none left blank.

name = ("Bob")   # <-- STRING
name_valid = bool(name)
print(name_valid)

Output:

True

If the name is left blank:

name = ("")   # <-- STRING

name_valid = bool(name)
print(name_valid)

Output:

False

Above are examples of Explicit typecasting.  We manually change the data type of each variable.

Implicit typecasting is automatic – if we divide two variables, a ‘float’ and an ‘integer’, the integer will automatically be converted to a float.

x = 4
y = 2.0

z = x / y
print (z)

Output:

2.0

Exercise:

Write some code asking for the users age and then output a sentence detail how many years it will be before they can legally vote or consume alcohol in Australia.

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