How do I parse a string to a float or int?

The Problem

How do I parse a string to a float or int in Python?

For example, I have a string like “1337” or “13.37” and I want to parse it to an int or float data type.

The Solution

If your string input is clean and predictable, the easiest way to parse a string to a float or int is by using the float or int built-in modules.

To cast a string to a float:

my_float_str = "13.37"
my_float_float = float(my_float_str)
print(my_float_float)  # will print 13.37

To cast a string to an int:

my_int_str = "1337"
my_int_int = int(my_int_str)
print(my_int_int)  # will print 1337

In some situations, you may need to account for edge cases. For example, you can’t use the int module if your input contains non-numerical characters such as a period.

my_float_str = "13.37"

# do not do this
my_int_str = int(my_float_str)

This will result in the following error:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '13.37'

If you are happy to throw away the floating point component (that is, round down to the nearest integer), you can first cast the string to a float and then cast the resulting float to an int. For example:

my_float_str = "13.37"
my_int_str = int(float(my_float_str))
print(my_int_str)   # will print 13

Note that float will still throw an error if you try to parse a string with more than one period. For example:

float("123.456.789")

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: '123.456.789'

If your input is dirty or unpredictable, you’ll need to implement some additional error handling or add a data cleaning step before attempting to cast your data to different types. For example, you can use a try-except statement to catch a ValueError exception:

try:
    not_a_float = float("123.456.789")
except ValueError:
    print("Could not parse string to float")