[Tutor] Some questions about my yen-USD.py

[Dick Moores]

I'm baaaack!

I kept getting ideas for what I (and some of you) thought was a 
finished yen-USD.py. And some of the good advice I got was to move on 
to other things. I did for a while, but I kept thinking up new 
revisions. The script has more than doubled in length. I'd previously 
posted v4 at <http://www.rcblue.com/Python/yen-USD-v3.txt>.

Here's v10: <http://www.rcblue.com/Python/yen-USD-v10.txt>

New functions:
again()
divide2StringDecimals()
multiply2StringDecimals()
roundNumber() -- replaced setPrecision()
printVariablesNotChanging()
formatNumber()
removeCommasFromNumbers()

rather radically revised function:
again()  -- offers several more choices

The most important change is that because I realized I wanted the 
program to be a general solution and give accurate answers for even 
very large amounts of Yen or USD, I decided to operate with (number) 
strings only, except when necessary in getRate() and getAmount() to 
error check user inputs. Those floats are not used in the 
calculations of Yen or USD.

The most difficult function for me to write was roundNumber(), which 
of course couldn't rely on the use of the built-in round() or the 
formatting of strings (see the line "format = "%." + str(precision) + 
'f'" in setPrecision() in v3).  Lack of experience with the slicing 
of lists caused many headaches. I didn't succeed in debugging until I 
put in print statements wherever a value changes, and trying many 
different integer strings and places (the arguments of 
roundNumber()). A good lesson, I think.

I hope some of the Tutors will take a look at the new functions, 
especially roundNumber().
Did I just reinvent the wheel?
Should it be broken up into more sub-functions (there's only one now)?
It works, but is it Pythonic? Etc.

I'm also curious about multiply2StringDecimals() and divide2StringDecimals().
Again, am I reinventing the wheel with these?
Is there a simpler way to multiply and divide big decimals with precision?

Thanks in advance,

Dick Moores