Use examples when they help make things clearer.
In Python 3.10, a new feature called pattern matching has been introduced which allows you to match values against patterns using syntax similar to switch statements in other languages like C or Java. This can help simplify code by replacing complex if-else chains with more concise and readable expressions. In this tutorial, we’ll explore how to use pattern matching through examples and explanations.
First, let’s start by installing Python 3.10 if you haven’t already done so. You can download the latest version from the official website or use a package manager like Homebrew on macOS or apt-get on Ubuntu to add it to your system. Once installed, open up a new terminal window and run python –version to confirm that you have Python 3.10 installed:
# This script checks the version of Python installed on the system
# To run this script, open a terminal window and type "python --version"
# The output should show the version of Python installed on the system
# If the output does not show Python 3.10.2, then the user may need to install the latest version
# To install the latest version of Python, the user can download it from the official website or use a package manager like Homebrew on macOS or apt-get on Ubuntu
# Once installed, the user can run "python --version" again to confirm the installation
# The output should now show Python 3.10.2
# This script is useful for checking the version of Python installed on the system and ensuring that the latest version is being used
# It can also be used to troubleshoot any issues related to Python version compatibility
# Import the necessary libraries for the script to run
import os
import sys
# Use the "python --version" command to check the version of Python installed on the system
os.system("python --version")
# The output should show the version of Python installed on the system
# If the output does not show Python 3.10.2, then the user may need to install the latest version
# To install the latest version of Python, the user can download it from the official website or use a package manager like Homebrew on macOS or apt-get on Ubuntu
# Once installed, the user can run "python --version" again to confirm the installation
# The output should now show Python 3.10.2
Now Let’s get cracking with pattern matching by looking at some examples. In this first example, we’ll use literal patterns to match a specific name and print out a greeting based on the result:
# This script uses pattern matching to print a greeting based on a given name.
# Define the name variable
name = "Guido"
# Use the match statement to compare the name variable to different patterns
match name:
# If the name matches "Guido", print a specific greeting
case "Guido":
print("Hello, Guido!")
# If the name does not match "Guido", use a wildcard pattern to match any other value
case _:
# Use f-strings to insert the name variable into the greeting
print(f"Hi there, {name}!")
In this example, we’re using the match statement to perform a pattern matching operation on the variable name. The first case matches the literal string “Guido”, and if it does, we print out a greeting that includes Guido’s name. If the value of name is not equal to “Guido”, then the second case will be executed instead, which uses a wildcard pattern (_) to match any other value and prints out a generic greeting using f-strings.
One limitation with structural pattern matching in Python 3.10 is that you can’t directly match values stored in variables. For example:
# This script is attempting to use structural pattern matching in Python 3.10 to match a value stored in the variable "bdfl" and print a greeting if the value is "Guido". However, this is not possible in Python 3.10 and will result in an error.
bdfl = "Guido"
# Use an if statement to check if the value of "bdfl" is "Guido"
if bdfl == "Guido":
# If the value is "Guido", print the greeting
print("Hello, Guido!")
# Another option is to use a dictionary to store the possible values and their corresponding greetings, and then use the "get" method to retrieve the greeting based on the value of "bdfl".
# Create a dictionary with the possible values and their corresponding greetings
greetings = {
"Guido": "Hello, Guido!"
}
# Use the "get" method to retrieve the greeting based on the value of "bdfl"
print(greetings.get(bdfl))
# However, this will still result in an error if the value of "bdfl" is not in the dictionary. To handle this, we can use the "get" method with a default value to print a generic greeting if the value is not found in the dictionary.
# Use the "get" method with a default value to retrieve the greeting based on the value of "bdfl"
print(greetings.get(bdfl, "Hello, there!"))
In this example, we’re trying to match the value stored in the variable bdfl using a pattern matching operation. However, since we haven’t defined any patterns for this specific value, Python will raise an error:
# This script is attempting to match the value stored in the variable "bdfl" using a pattern matching operation.
# However, since no patterns have been defined for this specific value, Python will raise a ValueError.
# Define a list of patterns to match against the value stored in "bdfl"
patterns = ["Guido", "Monty", "Python"]
# Use a for loop to iterate through each pattern in the list
for pattern in patterns:
# Check if the current pattern matches the value stored in "bdfl"
if pattern == bdfl:
# If there is a match, print a success message and break out of the loop
print("Match found for pattern: " + pattern)
break
# If no match is found after iterating through all patterns, raise a ValueError
else:
raise ValueError("No case matched: " + bdfl)
To work around this limitation, you can use a value pattern to match stored values instead of literal strings. A value pattern looks like a capture pattern but uses a previously defined dotted name that holds the value that will be matched against. For example:
# Import the Enum class from the enum module
from enum import Enum
# Create a class called BDFL that inherits from the Enum class
class BDFL(Enum):
# Define a constant GUIDO with the value "Guido"
GUIDO = "Guido"
# Use a value pattern to match stored values instead of literal strings
# A value pattern looks like a capture pattern but uses a previously defined dotted name that holds the value that will be matched against
# In this case, we are matching against the BDFL class
# The match statement allows us to perform pattern matching on the given value
# The := operator assigns the matched value to the variable bdfl
match bdfl := BDFL: # this works!
# Use the case statement to specify the different cases to match against
# In this case, we are matching against the GUIDO constant of the BDFL class
case BDFL.GUIDO:
# Print a greeting message for Guido
print("Hello, Guido!")
In this example, we’re using an enumeration class called BDFL to define a dotted name for the value “Guido”. We then use that dotted name in our pattern matching operation instead of a literal string.