Let’s talk about packing and unpacking arguments in Python! This might sound like a fancy term for something simple, but it can save us time and make our code more concise.
To set the stage: what are we talking about? Packing involves taking multiple values (like from a list) and converting them into a single tuple with fewer elements by leaving out some values. Unpacking is when we take one tuple or list and assign its values to multiple variables at once.
Let’s say you have a function that takes four arguments: `my_function(arg1, arg2, arg3, arg4)`. If you want to call this function with a list of arguments (`args = [val1, val2, val3, val4]`) instead of writing out each argument separately like so:
# Define a function called my_function that takes in four arguments
def my_function(arg1, arg2, arg3, arg4):
# Print the values of the four arguments
print(arg1, arg2, arg3, arg4)
# Create a list of arguments
args = [val1, val2, val3, val4]
# Call the function using the list of arguments
# Use the asterisk operator to unpack the list and pass each value as a separate argument
my_function(*args)
# Output: val1 val2 val3 val4
# The function takes in four arguments and prints them out
# The list of arguments is unpacked using the asterisk operator and passed as separate arguments to the function
You can use packing to create a tuple with the same values as your list and then pass that tuple into `my_function()`. Here’s an example:
# Create a tuple with the same values as the list using packing
# and pass it into my_function
# Example:
# list = [1, 2]
# tuple = (1, 2)
# my_function(tuple)
# Create a tuple with the first two elements of the list
packed_tuple = (args[0], args[1])
# Pass the tuple into my_function
my_function(packed_tuple)
This is like saying “take the first two elements of my list, put them in a new tuple called `packed_tuple`, and then pass that tuple into `my_function()`.”
Now unpacking. Let’s say you have a function that takes four arguments: `my_function(arg1, arg2, arg3, arg4)`. If you want to call this function with a list of arguments (`args = [val1, val2, val3, val4]`) instead of writing out each argument separately like so:
# This script is calling the function `my_function()` with four arguments: x, y, z, and w.
# However, it is not clear what values these arguments should have.
# To fix this, we can assign values to each argument before calling the function.
# For example, we can assign the values 1, 2, 3, and 4 to x, y, z, and w respectively.
# We can also use unpacking to pass a list of arguments to the function instead of writing them out separately.
# To do this, we can create a list called `args` with the values we want to pass to the function.
# Then, we can use the `*` operator to unpack the list and pass its values as arguments to the function.
# Finally, we can call the function with the unpacked arguments using the `my_function(*args)` syntax.
# Assigning values to the arguments
x = 1
y = 2
z = 3
w = 4
# Creating a list of arguments
args = [x, y, z, w]
# Calling the function with unpacked arguments
my_function(*args)
You can use unpacking to assign the values in your list to separate variables (like `x`, `y`, etc.) and then pass those variables into `my_function()`. Here’s an example:
# Assigning a list of values to a variable called args
args = [val1, val2, val3, val4]
# Unpacking the values in the args list and assigning them to separate variables
# x, y, z, and w
x, y, z, w = args
# Calling the function my_function and passing in the unpacked variables as arguments
my_function(x, y, z, w)
This is like saying “take the first value of my list and put it in a new variable called `x`, then take the second value and put it in a new variable called `y`, etc., and finally pass those variables into `my_function()`.”
It might seem like a small thing, but these techniques can save us time and make our code more concise and readable.