Add illustration of error handling

Author: gjbex

source-code/README.md

@@ -31,3 +31,4 @@ was used to develop it.
    structures.
 1. `code-organization`: illustration of how to organize code in packages
    and modules.
+1. `error-handling`: simple illustration of error handling.

source-code/error-handling/README.md

@@ -0,0 +1,10 @@
+# Error handling
+
+Illustrations of error handling.
+
+## What is it?
+
+1. `simple.py`: Python scripts that illustrates some
+   ways ot handle errors.
+1. `data.txt`: data file to use as input.
+1. `data_not_ok.txt`: incorrect data file to use as input.

source-code/error-handling/data.txt

@@ -0,0 +1,2 @@
+3.7
+3.3

source-code/error-handling/data_not_ok.txt

@@ -0,0 +1,4 @@
+3.7
+5.1
+some_string
+5.2

source-code/error-handling/simple.py

@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+import sys
+
+ARG_ERROR = 1
+FILE_ERROR = 2
+DATA_ERROR = 3
+
+def sum_numbers(file):
+    total = 0
+    for line in file:
+        total += float(line)
+    return total
+
+
+if __name__ == '__main__':
+    if len(sys.argv) < 2:
+        print('### error: no argument given', file=sys.stderr)
+        sys.exit(ARG_ERROR)
+    file_name = sys.argv[1]
+    try:
+        file = open(file_name, 'r')
+        print(sum_numbers(file))
+    except IOError as e:
+        print(f'### IO Error on {e.filename}: {e.strerror}')
+        sys.exit(FILE_ERROR)
+    except ValueError:
+        print(f'### Data Error on {file_name}: should contain only numbers')
+        sys.exit(DATA_ERROR)