int and long were "unified" a few versions back. Before that it was possible to overflow an int through math ops.

3.x has further advanced this by eliminating long altogether and only having int.

• Python 2: sys.maxint contains the maximum value a Python int can hold.
  • On a 64-bit Python 2.7, the size is 24 bytes. Check with sys.getsizeof().
• Python 3: sys.maxsize contains the maximum size in bytes a Python int can be.
  • This will be gigabytes in 32 bits, and exabytes in 64 bits.
  • Such a large int would have a value similar to 8 to the power of sys.maxsize.

It does exactly what it says - converts a string to integer in a given numeric base. As per the documentation, int() can convert strings in any base from 2 up to 36. On the low end, base 2 is the lowest useful system; base 1 would only have "0" as a symbol, which is pretty useless for counting. On the high end, 36 is chosen arbitrarily because we use symbols from "0123456789abcdefghijklmnopqrstuvwxyz" (10 digits + 26 characters) - you could continue with more symbols, but it is not really clear what to use after z.

"Normal" math is base-10 (uses symbols "0123456789"):

int("123", 10)  # == 1*(10**2) + 2*(10**1) + 3*(10**0) == 123

Binary is base-2 (uses symbols "01"):

int("101", 2)   # == 1*(2**2) + 0*(2**1) + 1*(2**0) == 5

"3" makes no sense in base 2; it only uses symbols "0" and "1", "3" is an invalid symbol (it's kind of like trying to book an appointment for the 34th of January).

int("333", 4)   # == 3*(4**2) + 3*(4**1) + 3*(4**0)
                # == 3*16 + 3*4 + 3*1
                # == 48 + 12 + 3
                # == 63

As the other answers have mentioned, the int operation will crash if the string input is not convertible to an int (such as a float or characters). What you can do is use a little helper method to try and interpret the string for you:

def interpret_string(s):
    if not isinstance(s, basestring):
        return str(s)
    if s.isdigit():
        return int(s)
    try:
        return float(s)
    except ValueError:
        return s

So it will take a string and try to convert it to int, then float, and otherwise return string. This is more just a general example of looking at the convertible types. It would be an error for your value to come back out of that function still being a string, which you would then want to report to the user and ask for new input.

Maybe a variation that returns None if its neither float nor int:

def interpret_string(s):
    if not isinstance(s, basestring):
        return None
    if s.isdigit():
        return int(s)
    try:
        return float(s)
    except ValueError:
        return None

val=raw_input("> ")
how_much=interpret_string(val)
if how_much is None:
    # ask for more input? Error?