Converting number in scientific notation to int

Question

Could someone explain why I can not use int() to convert an integer number represented in string-scientific notation into a python int?

For example this does not work:

print int('1e1')

But this does:

print int(float('1e1'))

print int(1e1)  # Works

Why does int not recognise the string as an integer? Surely its as simple as checking the sign of the exponent?

Answer 1

Behind the scenes a scientific number notation is always represented as a float internally. The reason is the varying number range as an integer only maps to a fixed value range, let's say 2^32 values. The scientific representation is similar to the floating representation with significant and exponent. Further details you can lookup in https://en.wikipedia.org/wiki/Floating_point.

You cannot cast a scientific number representation as string to integer directly.

print int(1e1)  # Works

Works because 1e1 as a number is already a float.

>>> type(1e1)
<type 'float'>

Back to your question: We want to get an integer from float or scientific string. Details: https://docs.python.org/2/reference/lexical_analysis.html#integers

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

For float or scientific representations you have to use the intermediate step over float.

Answer 2

Very Simple Solution

print(int(float(1e1)))

Steps:- 1- First you convert Scientific value to float. 2- Convert that float value to int . 3- Great you are able to get finally int data type.

Enjoy.

Answer 3

Because in Python (at least in 2.x since I do not use Python 3.x), int() behaves differently on strings and numeric values. If you input a string, then python will try to parse it to base 10 int

int ("077")
>> 77

But if you input a valid numeric value, then python will interpret it according to its base and type and convert it to base 10 int. then python will first interperet 077 as base 8 and convert it to base 10 then int() will jsut display it.

int (077)  # Leading 0 defines a base 8 number.
>> 63
077 
>> 63

So, int('1e1') will try to parse 1e1 as a base 10 string and will throw ValueError. But 1e1 is a numeric value (mathematical expression):

1e1
>> 10.0

So int will handle it as a numeric value and handle it as though, converting it to float(10.0) and then parse it to int. So Python will first interpret 1e1 since it was a numric value and evaluate 10.0 and int() will convert it to integer.

So calling int() with a string value, you must be sure that string is a valid base 10 integer value.

Answer 4

int(float(1e+001)) will work.

Whereas like what others had mention 1e1 is already a float.