Considering migrating to Python from Visual Basic 6 for engineering applications

Chris Angelico rosuav at
Mon Feb 22 08:09:08 EST 2016

On Mon, Feb 22, 2016 at 11:51 PM, BartC <bc at> wrote:
> Yes, I mentioned that point. In the OP's language, the variables can be
> declared as a particular type; in Python they could perhaps be 'declared' by
> first assigning with 0, 0.0 or "" for example. But that would need reference
> parameters to make use of tidily.

What you could do is something like this:

def read_values(file, values):
    """Read one line from file and parse it into the given list.

    Prepopulate values with a series of types or instances of types.
    The line of text read will be parsed accordingly.

    Returns the number of elements successfully read.
    line = file.readline()
    for idx, val in enumerate(values):
        if not isinstance(val, type):
            val = type(val)
        # Now add the logic to read an int, a float,
        # a str, a Fraction, etc etc etc, from the line,
        # breaking out of the loop if one can't be
        # read, and stashing the result into values[idx]
        # if it can.
    return idx

with open("inputfile") as f:
    values = [int, int, float, Fraction, str]
    while read_values(f, values) == 5:
        [index, level, percent, ratio, message] = values

This lets you "declare" the values' types, and use an input/output
parameter. It's not exactly the most Pythonic of techniques, but it
does kinda work. I suspect, though, that what you'd _really_ want is
something more like a sscanf string, or a "typed regex", which would
allow you to specify a bit more flexibly what you're looking for. You
could easily make a template string that has magic markers for "take
an integer", which would insert [0-9]+ (or something more elaborate)
and then capture it and call int() on the string before returning it.


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