Updated error handling example

Author: Arjan

8 - dealing with errors/advanced/logging-decorator.py

@@ -0,0 +1,52 @@
+import logging 
+from functools import wraps
+
+# Example from: https://www.geeksforgeeks.org/create-an-exception-logging-decorator-in-python/
+
+def create_logger(): 
+	
+	# create a logger object 
+	logger = logging.getLogger('exc_logger') 
+	logger.setLevel(logging.INFO) 
+	
+	#c reate a file to store all the 
+	# logged exceptions 
+	logfile = logging.FileHandler('exc_logger.log') 
+	
+	fmt = '%(asctime)s - %(name)s - %(levelname)s - %(message)s'
+	formatter = logging.Formatter(fmt) 
+	
+	logfile.setFormatter(formatter) 
+	logger.addHandler(logfile) 
+	
+	return logger 
+
+logger = create_logger() 
+
+# you will find a log file 
+# created in a given path 
+print(logger) 
+
+def exception(logger):
+    def decorator(func):
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            try:
+                return func(*args, **kwargs)
+            except:
+                issue = "exception in "+func.__name__+"\n"
+                issue = issue+"=============\n"
+                logger.exception(issue)
+                raise
+        return wrapper
+    return decorator 
+
+
+@exception(logger) 
+def divideByZero(): 
+	return 12/0
+
+# Driver Code 
+if __name__ == '__main__': 
+	divideByZero() 
+

8 - dealing with errors/advanced/retry-decorator.py

@@ -0,0 +1,51 @@
+import time
+import math
+from functools import wraps
+
+def retry(ExceptionToCheck, tries=4, delay=3, backoff=2, logger=None):
+    """Retry calling the decorated function using an exponential backoff.
+
+    http://www.saltycrane.com/blog/2009/11/trying-out-retry-decorator-python/
+    original from: http://wiki.python.org/moin/PythonDecoratorLibrary#Retry
+
+    :param ExceptionToCheck: the exception to check. may be a tuple of
+        exceptions to check
+    :type ExceptionToCheck: Exception or tuple
+    :param tries: number of times to try (not retry) before giving up
+    :type tries: int
+    :param delay: initial delay between retries in seconds
+    :type delay: int
+    :param backoff: backoff multiplier e.g. value of 2 will double the delay
+        each retry
+    :type backoff: int
+    :param logger: logger to use. If None, print
+    :type logger: logging.Logger instance
+    """
+    def deco_retry(f):
+
+        @wraps(f)
+        def f_retry(*args, **kwargs):
+            mtries, mdelay = tries, delay
+            while mtries > 1:
+                try:
+                    return f(*args, **kwargs)
+                except ExceptionToCheck as e:
+                    msg = "%s, Retrying in %d seconds..." % (str(e), mdelay)
+                    if logger:
+                        logger.warning(msg)
+                    else:
+                        print(msg)
+                    time.sleep(mdelay)
+                    mtries -= 1
+                    mdelay *= backoff
+            return f(*args, **kwargs)
+
+        return f_retry  # true decorator
+
+    return deco_retry
+
+@retry(Exception, tries=4)
+def test_fail(text):
+    raise Exception("Fail")
+
+test_fail("it works!")

8 - dealing with errors/after-context/__pycache__/db.cpython-39.pyc

@@ -0,0 +1,58 @@
+import sqlite3
+
+class SQLite():
+    def __init__(self, file='application.db'):
+        self.file=file
+    def __enter__(self):
+        self.conn = sqlite3.connect(self.file)
+        return self.conn.cursor()
+    def __exit__(self, type, value, traceback):
+        print("Closing the connection")
+        self.conn.close()
+
+class NotFoundError(Exception):
+    pass
+
+class NotAuthorizedError(Exception):
+    pass
+
+def blog_lst_to_json(item):
+    return { 
+        'id': item[0],
+        'published': item[1],
+        'title': item[2],
+        'content': item[3],
+        'public': bool(item[4])
+         }
+
+def fetch_blogs():
+    try:
+        with SQLite('application.db') as cur:
+
+            # execute the query
+            cur.execute('SELECT * FROM blogs where public=1')
+
+            # fetch the data and turn into a dict
+            return list(map(blog_lst_to_json, cur.fetchall()))
+    except Exception as e:
+        print(e)
+        return []
+
+def fetch_blog(id: str):
+    try:
+        with SQLite('application.db') as cur:
+
+            # execute the query and fetch the data
+            cur.execute(f"SELECT * FROM blogs where id='{id}'")
+            result = cur.fetchone()
+
+            # return the result or raise an error
+            if result is None:
+                raise NotFoundError(f'Unable to find blog with id {id}.')
+        
+            data = blog_lst_to_json(result)
+            if not data['public']:
+                raise NotAuthorizedError(f'You are not allowed to access blog with id {id}.')
+            return data
+    except sqlite3.OperationalError:
+        raise NotFoundError(f'Unable to find blog with id {id}.')

8 - dealing with errors/after-context/__pycache__/error-handling.cpython-39.pyc

@@ -0,0 +1,10 @@
+import sqlite3
+
+class SQLite():
+    def __init__(self, file='application.db'):
+        self.file=file
+    def __enter__(self):
+        self.conn = sqlite3.connect(self.file)
+        return self.conn.cursor()
+    def __exit__(self, type, value, traceback):
+        self.conn.close()

8 - dealing with errors/application.db renamed to 8 - dealing with errors/after-context/application.db

@@ -1,6 +1,5 @@
 from flask import Flask, jsonify, abort
-import sqlite3
-from db import fetch_blogs, fetch_blog, NotFoundError
+from db import fetch_blogs, fetch_blog, NotFoundError, NotAuthorizedError
 
 app = Flask(__name__)
 
@@ -18,3 +17,5 @@ def get_blog(id):
         return jsonify(fetch_blog(id))
     except NotFoundError:
         abort(404, description="Resource not found")
+    except NotAuthorizedError:
+        abort(403, description="Access denied")