Type Conversion

So far we have looked at three variable types: integers, floats and strings; and how to check what type a variable is.

Sometimes we want to convert between different variable types. To do this we can use the int, float and str functions:

int_var = 1
print(int_var, type(int_var))

float_var = float(int_var)
print(float_var, type(float_var))

1 <class 'int'>
1.0 <class 'float'>

float_var = 5.7
print(float_var, type(float_var))

int_var = int(float_var)
print(int_var, type(int_var))

5.7 <class 'float'>
5 <class 'int'>

Note that when you convert a float to an integer Python does simply discards the decimal part (if you wish to round-off a float you can use the round function).

str_var = '1.43'
print(str_var, type(str_var))

float_var = float(str_var)
print(float_var, type(float_var))

1.43 <class 'str'>
1.43 <class 'float'>

str_var = '12'
print(str_var, type(str_var))

int_var = int(str_var)
print(int_var, type(int_var))

12 <class 'str'>
12 <class 'int'>

Note that anything other than a number cannot be converted from a string to a float or int:

str_var = 'not a number'
print(str_var, type(str_var))

float_var = float(str_var)
print(float_var, type(float_var))

not a number <class 'str'>

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[5], line 4
      1 str_var = 'not a number'
      2 print(str_var, type(str_var))
----> 4 float_var = float(str_var)
      5 print(float_var, type(float_var))

ValueError: could not convert string to float: 'not a number'

Even strings that contain a number with a decimal part cannot be converted to an integer:

str_var = '4.563'
print(str_var, type(str_var))

int_var = int(str_var)
print(int_var, type(int_var))

4.563 <class 'str'>

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[6], line 4
      1 str_var = '4.563'
      2 print(str_var, type(str_var))
----> 4 int_var = int(str_var)
      5 print(int_var, type(int_var))

ValueError: invalid literal for int() with base 10: '4.563'