Core Python Programming (2nd Edition)

eturn retval
Upon running our new code, we obtain the following (different) messages when providing improper input
to safe_float(), even if both exceptions are managed by the same handler:
>>> safe_float('xyz')
'invalid literal for float(): xyz'
>>> safe_float({})
'object can't be converted to float'
10.3.7. Using Our Wrapped Function in an Application
We will now feature safe_float() in a mini application that takes a credit card transaction data file
(carddata.txt) and reads in all transactions, including explanatory strings. Here are the contents of our
example carddata.txt file:
% cat carddata.txt
# carddata.txt
previous balance
25
debits
21.64
541.24
25
credits
-25
-541.24
finance charge/late fees
7.30
5
Our program, cardrun.py, is given in Example 10.1.
Example 10.1. Credit Card Transactions (cardrun.py)
We use safe_float() to process a set of credit card transactions given in a file and read in as
strings. A log file tracks the processing.
1 #!/usr/bin/env python
2
3 def safe_float(obj):
4 'safe version of float()'
5 try:
6 retval = float(obj)
7 except (ValueError, TypeError), diag:
8 retval = str(diag)
9 return retval
10
11 def main():
12 'handles all the data processing'