Initial commit

Exercises/ex5_5.md

@@ -0,0 +1,97 @@
+\[ [Index](index.md) | [Exercise 5.4](ex5_4.md) | [Exercise 5.6](ex5_6.md) \]
+
+# Exercise 5.5
+
+*Objectives:*
+
+- Learn more about exception handling and logging
+
+*Files Modified:* `reader.py`
+
+In the `reader.py` file, there is a central function `convert_csv()` that does
+most of the work.  This function crashes if you run it on data with missing or
+bad data.  For example:
+
+```python
+>>> port = read_csv_as_dicts('Data/missing.csv', types=[str, int, float])
+Traceback (most recent call last):
+  File "<stdin>", line 1, in <module>
+  File "reader.py", line 24, in read_csv_as_dicts
+    return csv_as_dicts(file, types, headers=headers)
+  File "reader.py", line 13, in csv_as_dicts
+    lambda headers, row: { name: func(val) for name, func, val in zip(headers, types, row) })
+  File "reader.py", line 9, in convert_csv
+    return list(map(lambda row: converter(headers, row), rows))
+  File "reader.py", line 9, in <lambda>
+    return list(map(lambda row: converter(headers, row), rows))
+  File "reader.py", line 13, in <lambda>
+    lambda headers, row: { name: func(val) for name, func, val in zip(headers, types, row) })
+  File "reader.py", line 13, in <dictcomp>
+    lambda headers, row: { name: func(val) for name, func, val in zip(headers, types, row) })
+ValueError: invalid literal for int() with base 10: ''
+>>> 
+```
+
+## (a) Catching Exceptions
+
+Instead of crashing on bad data, modify the code to issue a warning message
+instead. The final result should be a list of the rows that were successfully
+converted. For example:
+
+```python
+>>> port = read_csv_as_dicts('Data/missing.csv', types=[str, int, float])
+Row 4: Bad row: ['C', '', '53.08']
+Row 7: Bad row: ['DIS', '50', 'N/A']
+Row 8: Bad row: ['GE', '', '37.23']
+Row 13: Bad row: ['INTC', '', '21.84']
+Row 17: Bad row: ['MCD', '', '51.11']
+Row 19: Bad row: ['MO', '', '70.09']
+Row 22: Bad row: ['PFE', '', '26.40']
+Row 26: Bad row: ['VZ', '', '42.92']
+>>> len(port)
+20
+>>>
+```
+
+Note:  Making this change may be a bit tricky because of your previous use of the `map()`
+built-in function. You may have to abandon that approach since there's no easy way to catch
+and handle exceptions in `map()`.
+
+## (b) Logging
+
+Modify the code so that warning messages are issued using the `logging` module.  In 
+addition, give optional debugging information indicating the reason for failure.
+For example:
+
+```python
+>>> import reader
+>>> import logging
+>>> logging.basicConfig(level=logging.DEBUG)
+>>> port = reader.read_csv_as_dicts('Data/missing.csv', types=[str, int, float])
+WARNING:reader:Row 4: Bad row: ['C', '', '53.08']
+DEBUG:reader:Row 4: Reason: invalid literal for int() with base 10: ''
+WARNING:reader:Row 7: Bad row: ['DIS', '50', 'N/A']
+DEBUG:reader:Row 7: Reason: could not convert string to float: 'N/A'
+WARNING:reader:Row 8: Bad row: ['GE', '', '37.23']
+DEBUG:reader:Row 8: Reason: invalid literal for int() with base 10: ''
+WARNING:reader:Row 13: Bad row: ['INTC', '', '21.84']
+DEBUG:reader:Row 13: Reason: invalid literal for int() with base 10: ''
+WARNING:reader:Row 17: Bad row: ['MCD', '', '51.11']
+DEBUG:reader:Row 17: Reason: invalid literal for int() with base 10: ''
+WARNING:reader:Row 19: Bad row: ['MO', '', '70.09']
+DEBUG:reader:Row 19: Reason: invalid literal for int() with base 10: ''
+WARNING:reader:Row 22: Bad row: ['PFE', '', '26.40']
+DEBUG:reader:Row 22: Reason: invalid literal for int() with base 10: ''
+WARNING:reader:Row 26: Bad row: ['VZ', '', '42.92']
+DEBUG:reader:Row 26: Reason: invalid literal for int() with base 10: ''
+>>>
+```
+
+\[ [Solution](soln5_5.md) | [Index](index.md) | [Exercise 5.4](ex5_4.md) | [Exercise 5.6](ex5_6.md) \]
+
+----
+`>>>` Advanced Python Mastery  
+`...` A course by [dabeaz](https://www.dabeaz.com)  
+`...` Copyright 2007-2023  
+
+![](https://i.creativecommons.org/l/by-sa/4.0/88x31.png). This work is licensed under a [Creative Commons Attribution-ShareAlike 4.0 International License](http://creativecommons.org/licenses/by-sa/4.0/)