Toolbox #2 - Pickling

pickling_code.py

@@ -0,0 +1,56 @@
+""" A program that stores and updates a counter using a Python pickle file"""
+
+from os.path import exists
+import sys
+from pickle import dump, load
+
+def update_counter(file_name, reset=False):
+    if exists(file_name) == True and reset == False: #checks if file exists and reset is False
+        f = open(file_name, 'r+') #opens file in read + mode
+        counter = load(f) + 1 #iterates counter in existing file
+        f.seek(0,0) #moves file handle to beginning of file
+        dump(counter, f) #stores new counter value in the file
+    else:
+        f = open(file_name, 'w') #creates new file in writing mode
+        counter = 1 #initializes counter to 1
+        dump(counter,f) #stores counter in the file
+    return counter
+    f.close() #closes file
+
+#testing the counter function
+update_counter('potato.txt', True)
+update_counter('potato.txt')
+update_counter('banana.txt', True)
+update_counter('banana.txt')
+update_counter('potato.txt')
+
+""" Updates a counter stored in the file 'file_name'
+
+		A new counter will be created and initialized to 1 if none exists or if
+		the reset flag is True.
+
+		If the counter already exists and reset is False, the counter's value will
+		be incremented.
+
+		file_name: the file that stores the counter to be incremented.  If the file
+				   doesn't exist, a counter is created and initialized to 1.
+		reset: True if the counter in the file should be rest.
+		returns: the new counter value
+
+	>>> update_counter('blah.txt',True)
+	1
+	>>> update_counter('blah.txt')
+	2
+	>>> update_counter('blah2.txt',True)
+	1
+	>>> update_counter('blah.txt')
+	3
+	>>> update_counter('blah2.txt')
+	2
+	"""
+if __name__ == '__main__':
+	if len(sys.argv) < 2:
+		import doctest
+		doctest.testmod()
+	else:
+		print "new value is " + str(update_counter(sys.argv[1]))