Computer Programming Unit 2 Tuples Tutorial Directions
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- Navigate this page:
- Introducing the Hero’s Inventory Program
- Treating a Tuple as a Condition
- Creating a Tuple with Elements
- Introducing the Hero’s Inventory 2.0
- Using the len() Function with Tuples
- Using the in Operator with Tuples
- Understanding Tuple Immutability
| Computer Programming
Unit 2
Tuples Tutorial Directions: Read the following Tutorial THOUROUGHLY. Be sure to work through ALL of the examples. You will need to know how to apply these concepts to your own programs. Creating Tuples Tuples are a type of sequence, like strings. But unlike string, which can only contain characters, tuples can contain elements of any type. That means you can have a tuple that stores a bunch of high scores for a game, or one that stores a group of employee names. The nice thing about tuples is that they don’t have to be all of the same type. You can create a tuple with both strings and numbers, if you wanted. And you don’t have to stop at strings and numbers. You can create a tuple that contains a sequence of graphic images, sound files, or even a group of aliens (you’ll learn this later). Whatever you can assign to a variable, you can group together and store as a sequence in a tuple. Introducing the Hero’s Inventory Program Hero’s Inventory maintains the inventory of a hero from a typical role-playing game. Like most role-playing games ever created, the hero is from a small, insignificant village. His father was, of course, killed by an evil warlord. And now the hero has come of age. It’s time for him to seek his revenge. In this program, the hero’s inventory is represented by a tuple. The tuple contains strings, one for each item in the hero’s possession. The hero starts out with nothing, but then I give him a few items. Here is the code: # Name # September 30, 2009 # heroInventory.py # create an empty tuple def main(): inventory = () # treat the tuple as a condition if not inventory: print "You are empty-handed."
inventory = ("sword", "armor", "shield", "healing potion")
print "\nThe tuple inventory is:\n", inventory # print each element in the tuple print "\nYour items:" for item in inventory: print item raw_input("\n\nPress the enter key to exit.") main() Creating an Empty Tuple To create a tuple you just surround a sequence of values, separated by commas, with parentheses. Even a pair of lone parentheses is a valid (but empty) tuple. I created an empty tuple in the first part of the program to represent that the hero has nothing: inventory = () Treating a Tuple as a Condition When you learn about conditions, you saw that you could treat any value in Python as a condition. That means you can treat a tuple as a condition, too. And that’s what I did in the next line: if not inventory: print "You are empty-handed." As a condition, an empty tuple is false. A tuple with at least one element is true. Because the tuple assigned to inventory is empty, it’s false. That means that not inventory is true. So the computer goes into the if statement and prints the string, “You are empty-handed.” Creating a Tuple with Elements An unarmed hero is a boring hero. So next, I created a new tuple with string elements that represent useful items for our hero. I assigned this new tuple to inventory with the following lines: inventory = ("sword", "armor",
"shield", "healing potion") Each element in the tuple is separated by a comma. That makes the first element the string “sword”, the next “armor”, the next “shield”, and the last element “healing potion”. So each string is a single element in the tuple. Also notice that the tuple spans multiple lines. You can write a tuple in one line or span it across multiple lines like I did, as long as you end each line after a comma. Printing a Tuple Though a tuple can contain many elements, you can print the entire tuple just like you would any single value. That’s what I did in the next line: print "\nThe tuple inventory is:\n", inventory The computer displays all the elements, surrounded by parentheses. Looping through a Tuple’s Elements Finally, I wrote a for loop to march through the elements in inventory and print each one individually: print "\nYour items:" for item in inventory: print item
# September 30, 2009 # heroInventory2.py # Demonstrates tuples # create a tuple with some items and display with a for loop def main(): inventory = ("sword", "armor", "shield", "healing potion") print "Your items:" for item in inventory: print item raw_input("\nPress the enter key to continue.") # get the length of a tuple print "You have", len(inventory), "items in your possession." raw_input("\nPress the enter key to continue.") # test for membership with in if "healing potion" in inventory: print "You will live to fight another day."
index = int(raw_input("\nEnter the index number for an item in inventory: ")) print "At index", index, "is", inventory[index]
begin = int(raw_input("\nEnter the index number to begin a slice: ")) end = int(raw_input("Enter the index number to end the slice: ")) print "inventory[", begin, ":", end, "]\t\t", print inventory[begin:end]
chest = ("gold", "gems") print "You find a chest. It contains:" print chest print "You add the contents of the chest to your inventory." inventory += chest print "Your inventory is now:" print inventory raw_input("\n\nPress the enter key to exit.") main() Using the len() Function with Tuples The len() function works with tuples just the way it does with strings. If you want to know the length of a tuple, place it inside the parantheses. The function returns the number of elements in the tuple. Empty tuples, or any empty sequence for that matter, have a length of 0. The following lines use the len() function with the tuple: # get the length of a tuple print "You have", len(inventory), "items in your possession." raw_input("\nPress the enter key to continue.") Because the tuple has four elements, the message You have 4 items in your possession, is displayed. Notice, in the tuple inventory, the string “healing potion” is counted as a single element even though it is two words. Using the in Operator with Tuples Just like with strings, you can use the in operator with tuples to test for element membership. And just like before, the in operator is usually used to create a condition. That’s how I used it here: # test for membership with in if "healing potion" in inventory: print "You will live to fight another day."
index = int(raw_input("\nEnter the index number for an item in inventory: ")) print "At index", index, "is", inventory[index]
Slicing Tuples Slicing works just like you saw with strings. You give a beginning and ending position. The result is a tuple containing every element between those two positions. Just as in the Pizza Slicer program from earlier, I let the user pick the beginning and ending position number. Then, like before, the program displays the slice: # display a slice begin = int(raw_input("\nEnter the index number to begin a slice: ")) end = int(raw_input("Enter the index number to end the slice: ")) print "inventory[", begin, ":", end, "]\t\t", print inventory[begin:end]
-4 -3 -2 -1 Understanding Tuple Immutability Like strings, tuples are immutable. That means you can’t change a tuple. Here’s an interactive session to prove my point: >>> inventory = ("sword", "armor", "shield", "healing potion") >>> print inventory ('sword', 'armor', 'shield', 'healing potion') >>> inventory [0] = "rope" Traceback (most recent call last): File "
inventory [0] = "rope" TypeError: 'tuple' object does not support item assignment Concatenating Tuples You can concatenate tuples the same way you concatenate strings. You can simply join them together with +, the concatenation operator: # concatinate two tuples chest = ("gold", "gems") print "You find a chest. It contains:" print chest print "You add the contents of the chest to your inventory." inventory += chest print "Your inventory is now:" print inventory raw_input("\n\nPress the enter key to exit.") The first thing I did was create a new tuple, chest, with the two string element “gold” and “gems”. Next, I printed chest to show its elements. After that, I used an augmented assignment operator to concatenate inventory with chest and assign the result back to invevntory. I did not modify the original tuple assigned to inventory (because that is imposible because tuples are immutable). Instead, the augmented assignment operator created a brand new tuple with the elements from inventory and chest and assigned that to inventory. Directory: file -> view view -> Western Europe after wwii view -> Author study: paul fleischman view -> Qpa1 7ela study Guide view -> Arctic Oil/Gas Neg view -> November 1970 Approximately 150,000-500,000 deaths Bhola Cyclone Bangladesh view -> Grade Level: 6 Unit of Study: Caribbean glce view -> Citation: Duffield, Katy view -> Table of Contents Lesson # view -> Chinese Wind Energy Disad Download 34.33 Kb. Share with your friends:
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