Python for AI: A Crash Course
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Instructions
Python’s design philosophy emphasizes simplicity, readability, and ease of use, making it an accessible language for both beginners and experienced developers. The Python community has adopted this philosophy for their code, and as a Python programmer, you’re encouraged to do the same. In this section, you’ll learn general guidelines and best practices to follow when writing your own Python programs by improving a couple of small Python apps.
The Zen Of Python And Pythonic Code
There’s an “Easter egg” built into Python. To see it, Open the checklist-starter.ipynb notebook. Enter the following into a new code cell and run it:
# Run me!
import this
PEP 8
The Zen of Python is a good read, but if you want more concrete guidance on writing Python code, you should consult the document known throughout the Python community as PEP 8.
Refactoring An App To Make It More Pythonic
It’s time to take a working app written in Python and refactor its code. Refactoring better utilizes Python’s features and follows the guidelines and practices of the Python community.
Using Brackets To Make Long Lines Readable
Find the code cell stating with the comment # Initial checklist. It contains a line that defines checklist, a list of ChecklistItem instances representing the contents of the checklist.
# Initial checklist
checklist = [
ChecklistItem("Clean the living room"),
ChecklistItem("Walk the dog", True, "high"),
ChecklistItem("Buy groceries"),
ChecklistItem("Make dinner", priority="high")
]
Putting A Comma After The Last Item In A List, Tuple, Set, Or Dictionary Literal
Add one more item to the end of checklist:
ChecklistItem("Fix toaster")
Using The __repr__() Method When Defining Classes
Confirm that the changes you made work by entering checklist into a new code cell and running it. If you get an error make sure you have run all the previous cells before running the newly created one. This will display the list’s contents, with each Checklistitem instance in the list represented by the output of the __repr__() method. Remember, __repr__() returns the developer-facing string representation of an instance.
Using Python’s Ternary Operator
Look at ChecklistItem’s __str__() method, which returns the user-facing string representation of an instance. It sets a variable named checkbox to a checked box emoji if the checklist item it represents is checked or a gray box emoji representing an unchecked box if it’s unchecked.
def __str__(self):
"""Return a user-friendly string representation of the item."""
return f"{"✅" if self.checked else "⬜️"} {self.name} {self.priority_emoji()}({self.priority})"
Using Truthy and Falsy Values To Make Code Concise
Go to the code cell where the display_checklist() function is defined. The function works, but it could be improved.
# Show the user the checklist
def display_checklist(checklist):
"""Show the user the checklist."""
if checklist:
item_number = 1
for item in checklist:
print(f"{item_number}: {item}")
item_number += 1
else:
print("The checklist is empty.")
Using enumerate() When Iterating To Get Both Index And Item
display_checklist() still has room for improvement. If checklist isn’t empty, the current code uses a for loop to iterate through the list items, and it also sets up the index variable to store the number of the item currently being printed. The index variable is incremented at the end of each iteration.
# Show the user the checklist
def display_checklist(checklist):
"""Show the user the checklist."""
if checklist:
for index, item in enumerate(checklist, start=1):
print(f"{index}: {item}")
else:
print("The checklist is empty.")
Maybe You Need An in, Not An or
Find the code cell where the add_item_to_checklist() function is defined. Note that after it gets the user’s input about the item’s priority, it performs three if comparisons joined by or operators to see if the user entered low, medium, or high. This would get unwieldy if there were more valid options.
def add_item_to_checklist(checklist):
"""
Get an item name and priority from the user
and add it to the checklist.
"""
while True:
name = input("What's the item's name?").strip()
if name:
break
print("Please enter a name for the item.")
while True:
priority = input("What's its priority (low, medium, or high)?").strip().lower()
if priority in ["low", "medium", "high"]:
break
else:
print("Please enter 'low', 'medium', or 'high'.")
new_item = ChecklistItem(name, False, priority)
checklist.append(new_item)
You Can Chain Comparisons
Go to the code cell containing the edit_item_in_checklist() function. After the line that asks the user which item they want to edit, there’s an if that compares the value of index to confirm that it’s between 0 as a lower bound and len(checklist) as an upper bound. Whenever you see this kind of comparison, chain them.
def edit_item_in_checklist(checklist):
if not checklist:
print("There are no items in the checklist. There's nothing to edit.")
return
print("Here are the items:")
display_checklist(checklist)
index = int(input("Which item do you want to edit?")) - 1
if 0 <= index < len(checklist):
while True:
name = input("What's the item's name?").strip()
if name:
break
print("Please enter a name for the item.")
while True:
priority = input("What do you want to change the priority to (low, medium, or high)?")
if priority in ["low", "medium", "high"]:
break
print("Please enter 'low', 'medium', or 'high'.")
checklist[index].name = name
checklist[index].priority = priority
Using f-strings Instead Of String Concatenation
Find the code cell where the delete_item_from_checklist() function is defined. Here’s the line in that function that builds the string asking the user if they’re sure they want to delete an item:
question = "Are you sure you want to delete " + checklist[index].name + "?"
def delete_item_from_checklist(checklist):
"""
Ask the user to select a checklist item,
then delete it if they're sure.
"""
if not checklist:
print("There are no items in the checklist. There's nothing to edit.")
return
print("Here are the items:")
display_checklist(checklist)
index = int(input("Which item do you want to delete?")) - 1
if 0 <= index < len(checklist):
question = f"Are you sure you want to delete {checklist[index].name}?"
answer = input(question).strip().lower()
if answer.lower() in ["y", "yes", "ok", "okey dokey"]:
deleted_item = checklist.pop(index)
print(f"Deleted {deleted_item.name}.")
Dictionaries Can Be Decision Makers
Run the cells containing check_item() and uncheck_item(). Scroll past them and find the cell containing main(), the app’s main function.
# Act on the user’s selection
ACTIONS = {
1: display_checklist,
2: check_item,
3: uncheck_item,
4: add_item_to_checklist,
5: edit_item_in_checklist,
6: delete_item_from_checklist,
}
print("\n")
if 1 <= choice <= 6:
ACTIONS[choice](checklist)
elif choice == 7:
print("Checklist main() finished.")
break
else:
print("Please enter a valid choice (1 - 7).")
print("\n")