float_fix.py

from tokenize import tokenize, untokenize, NUMBER, STRING, NAME, OP
from io import BytesIO


def float_to_decimal(s):
    """Substitute Decimals for floats in a string of statements.

    >>> from decimal import Decimal
    >>> s = 'print(+21.3e-5*-.1234/81.7)'
    >>> decistmt(s)
    "print (+Decimal ('21.3e-5')*-Decimal ('.1234')/Decimal ('81.7'))"

    The format of the exponent is inherited from the platform C library.
    Known cases are "e-007" (Windows) and "e-07" (not Windows).  Since
    we're only showing 12 digits, and the 13th isn't close to 5, the
    rest of the output should be platform-independent.

    >>> exec(s)  #doctest: +ELLIPSIS
    -3.21716034272e-0...7

    Output from calculations with Decimal should be identical across all
    platforms.

    >>> exec(decistmt(s))
    -3.217160342717258261933904529E-7
    """
    result = []
    g = tokenize(BytesIO(s.encode("utf-8")).readline)  # tokenize the string
    for toknum, tokval, _, _, _ in g:
        if toknum == NUMBER and "." in tokval:  # replace NUMBER tokens
            result.extend(
                [(NAME, "Decimal"), (OP, "("), (STRING, repr(tokval)), (OP, ")")]
            )
        else:
            result.append((toknum, tokval))
    return untokenize(result).decode("utf-8")