nano_parser.py

"""
"""

import operator as op


def eval_safer(s):
    """basic parsinig an evaluation of expressions."""
    ops = {'*': op.mul,
           '+': op.add,
           '-': op.sub,
           '/': op.truediv,
           '^': op.pow}
    # get the numbers at the start of the string
    current = []
    buffer = 0
    op_queued = None
    for idx, c in enumerate(s.replace(' ', '')):
        if c in '0123456789':
            current.append(c)
        elif s[idx] in ops:
            print('i saw you want a {}'.format(ops[s[idx]]))
            if op_queued:
                # could also be op.add from the beginning, but meh.
                buffer = op_queued(buffer, int(''.join(current)))
                print('buffer is now {}'.format(buffer))
            else:
                buffer = int(''.join(current))
                print('buffer is now {}'.format(buffer))
            op_queued = ops[s[idx]]
            current = []
        else:
            # return None on any unforseen character.
            return None
    if op_queued:  # some work left ?
        buffer = op_queued(buffer, int(''.join(current)))
    else:
        buffer = int(''.join(current))
    return buffer


def ask():
    while True:  # iterate until `break`
        in_usr = input("Please enter a positive integer: ")
        processed = eval_safer(in_usr)
        if isinstance(processed, (int, float)):
            break
        else:
            print("nah, try again.")
    print('you typed for {}'.format(processed))

if __name__ == '__main__':
    ask()