Python: Extract float from string of standard form

Question

I want to take a command line argument, argv[2] , which will always be of the form split_pct=x where x is a specified float. To clarify, here's some valid examples: split_pct=90.0 or split_pct=55.23 . For the given input, how could I extract that float?

Running Python 3.7

Answer 1

You want to look into type casting:

x = 1.0
y = 2*x # 2.0
z = 2/x # 2.0

x = str(1.0)
y = 2*x # TypeError: unsupported operand type(s) for /: 'int' and 'str'
z = 2/x # TypeError: unsupported operand type(s) for /: 'int' and 'str'

w = float(x) # Cast to float
y = 2*w # 2.0
z = 2/w # 2.0

More information can be found here .

To use an argument from the command line:

import sys
split_pct = sys.argv[2]

This works if your command is this:

python3 script.py first_var 90.0

Since the script name counts as sys.argv[0] , see here for more details:

Answer 2

Resolved - because the string is of a standard form, we can get only the values after split_pct= . split_pct= is 10 chars, so

x = float(sys.argv[2][10:]

works.