istr-python 0.0.3

istr is a module to use strings as if they were integers.

Introduction

The istr module has exactly one class: istr.

With this it is possible to interpret string as if they were integers.

This can be very handy for solving puzzles, but also for other purposes. For instance the famous send more money puzzle

  S E N D
  M O R E
--------- +
M O N E Y

can be nicely, albeit not very efficient, coded as:

import itertools
from istr import istr

for s, e, n, d, m, o, r, y in istr(itertools.permutations(range(10), 8)):
    if m and ((s | e | n | d) + (m | o | r | e) == (m | o | n | e | y)):
        print(f" {s|e|n|d}")
        print(f" {m|o|r|e}")
        print("-----")
        print(f"{m|o|n|e|y}")

And it is a nice demonstration of extending a class (str) with extra and changed functionality.

Installation

Installing istr with pip is easy.

$ pip install istr-python

or when you want to upgrade,

$ pip install istr-python --upgrade

Alternatively, istr.py can be just copied into you current work directory from GitHub (https://github.com/salabim/istr).

No dependencies!

Usage

Just start with

from istr import istr

Now we can define some istrs:

four = istr("4")
five = istr("5")

Them we can do

x= four * five

, after which x is istr("20")

And now we can do

print(x == 20)
print(x == "20")

resulting in two times True. That's because istr instances are treated as int, although they are strings.

That means that we can also say

print(x < 30)
print(x >= "10")

again resulting in two times True.

In contrast to an ordinary string

print(four + five)

prints 9, as istr are treated as ints.

So, how can we concatenate istrs? Just use the or operator (|):

print(four | five)

will output 45.

And the result is again an istr.

That means that

(four | five) / 3

is istr("9").

In order to multiply a string in the usual sense, you cannot use 3 * four, as that will be 12.

We use the matrix multiplication operator (@) for this. So 3 @ four is 444.

Also allowed are

abs(four)
-four 

The bool operator works for integer value of an istr. So bool('0') ==> False bool('1') ==> True

if istr('0'):
    print("True")
else:
    print("False")

this will print False

For the in operator a istr is treated as an ordinary string, although it is possible to use ints as well:

"34" in istr(1234)
34 in istr(1234)

On the left hand side an istr is always treated as a string:

istr(1234) in "01234566890ABCDEF"

Note that all calculations are strictly integer calculations. That means that if a float variale is ever produced it will be converted to an int. Also divisions are always floor divisions!

There's a special case for istr(""). This is a proper empty string, but also represents the value of 0. That is to allow for istr("").join(i for i in "01234)"

Sorting a list of istrs is based on the integer value, not the string. So

' '.join(sorted('1 3 2 4 5 6 11 7 9 8 10 12 0'.split()))

is

'0 1 10 11 2 3 4 5 6 7 8 9'

,whereas

' '.join(sorted(istr('1 3 2 4 5 6 11 7 9 8 10 12 0'.split())))

is

'0 1 2 3 4 5 6 7 8 9 10 11'

Using other values for istr than int or str

Apart from with simple int or str, istr can be initialized with

Additional methods

It is possible to test for even/odd with the

is_even and is_odd method, e.g.

print(istr(4).is_even())
print(istr(5).is_odd())

This will print True twice.

The method istr.reversed() will return the an istr with the reversed content:

print(repr(istr(456).reversed()))
print(repr(istr("0456").reversed()))

result:

istr('654')
istr('6540')

Note that is impossible to reverse a negative istr.

Subclassing istr