Considering migrating to Python from Visual Basic 6 for engineering applications

wrong.address.1 at gmail.com wrong.address.1 at gmail.com
Sat Feb 20 13:38:40 EST 2016


On Saturday, 20 February 2016 09:49:17 UTC+2, Larry Hudson  wrote:
> On 02/19/2016 10:14 AM, wrong.address.1 at gmail.com wrote:
> [snip]
> >
> > This is precisely reading one character at a time. If not exactly reading one character, it is effectively looking at each character to assemble the number. Not a good sign. I guess there might be libraries which will help read numbers better, but I would expect a good language to be able to handle this basic thing for engineers - to read numbers like Fortran and Basic do.
> >
> > Still, if I have misunderstood something, I will be glad to be corrected. I would generally know that the first three numbers will be floating point, the next will be something and then the next will be something else, etc. Does that help or does one still have to look at each character and determine how to place it in a number?
> >
> > Thanks for your patience. I don't want surprises later on, which is why I am asking very stupid questions.
> >
> It absolutely does NOT require reading a character at a time!  You are reading the data from a 
> text file, which means everything is a string.  These strings (or sub-strings) can represent 
> integers, floats, dates, phone numbers or whatever.  Your example data implies a free-form 
> style, where it is then necessary to determine the data type for each of these (sub)strings 
> individually.  Of course, if your data has a defined fixed format, this is simplified -- but 
> they are still initially strings that have to be converted.  String processing in Python is very 
> powerful and versatile.
> 
> BTW, it does no good to continue to think strictly in BASIC techniques.  Python is a different 
> language with a different approach to attacking problems.  If you try to write BASIC (or C or 
> Java or ...) programs in Python syntax you'll just get bad programs.  Forget trying to find 
> features in Python that are identical to the features of BASIC.  Python requires a different 
> mind-set to use it properly -- just like any other language.
> 
> Here is a rather naive somewhat brute-force way to read your example data.  I'm using a Python 
> list here to simulate the file reading.  (Actually, using read() instead of readline() will also 
> give this list.)  Python lists are essentially the same as arrays in other languages, but much 
> more powerful and versatile.  Two examples of the differences between arrays and lists are:  can 
> use mixed data types, you are not restricted to all the same data type, and the size of lists 
> are dynamic -- they grow or shrink as necessary.
> 
> Comments start with a #
> Strings in Python can be delimited by single-quotes ('), double-quotes (") or triple-quotes (""" 
> or ''').  Triple-quoted strings can be multi-line text.  The triple-quote here is used as what 
> Python calls a docstring, which it saves internally for documenting your program.
> 
> <code>
> #   Define a function to determine the data type a string represents
> def chktyp(s):
>      """Check string s for int, float or string.  Returns the data and a type code"""
>      try:
>          return int(s), 'int'      #  Try to convert to int, return it if successful
>      except ValueError:            #  No, it's not an int
>          pass                      #  Drop into float test
>      try:
>          return float(s), 'float'  #  Try to convert to float, return it if successful
>      except ValueError:            #  No, it's not a float
>          return s, 'str'           #  It must be a string
> 
> #   Here is your (simulated) data as a list of strings
> data = [
>      '2 12.657823 0.1823467E-04 114 0',
>      '3 4 5 9 11',
>      '"Lower"',                    #  Could be left simply as "Lower"
>      '278.15']
> 
> #   Process the data
> for line in data:                 #  For each line of the data
>      dat = line.split()            #  Make a list of the sub-strings in the line
>      for stng in dat:              #  For each substring
>          dt, tp = chktyp(stng)     #  Get the data and the type
>          print('{} is a {}'.format(dt, tp))    #  Print this data
> </code>
> 
> Running this example gives this result:
> 
> 2 is a int
> 12.657823 is a float
> 1.823467e-05 is a float
> 114 is a int
> 0 is a int
> 3 is a int
> 4 is a int
> 5 is a int
> 9 is a int
> 11 is a int
> "Lower" is a str
> 278.15 is a float
> 
> I hope this gives you a slight hint about the Python way of doing things.  Yes, of course it's 
> very different from BASIC, but if you can pick up on the Pythonic way of doing things I think 
> you might at least find it useful.
> 
>       -=- Larry -=-

I realise that this file i/o will have to be thought of in a different way if I start to use Python. This may still be worthwhile inspite of the complexity and loss in readability of the code.

To give an example of the kind of things I have to read (and I have to read numbers from several files usually), here is some VB6 code:

    Open "N020S.TXT" For Input As #8

    Input #8, ND, NIN, NT ' all integers
    Text9.Text = ND
    Text1 = CStr(NIN)
    Text4 = NT
    
    Text12 = ""
    For i = 1 To NIN
        Input #8, DINCOL(i) ' single precision floating point vector
        Text12 = Text12.Text & DINCOL(i) & " "
        If Dvarname(1) <> "" Then varname(i) = Dvarname(NLCOL(i)) ' strings
    Next i

    etc..

The data file (written by another VB6 code) contains in the first few lines:

 10            6             1 
8.65  0.2192347   3.33E-4    44     0.0051        6 
9 
 1 
2 1 
 3 

How complicated could this get in Python? Reading the numbers is one thing, and then placing the values in text boxes of the GUI. Or can I write my own reading subroutines which can then be called like 
ReadVBstyle 8, ND, NIN, NT 
to make the code more readable?


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