Popis Pythona dodati VS Proširenje popisa Python - Razlika objašnjena primjerima metoda niza

? Dobrodošli

Ako želite naučiti kako raditi s .append()a .extend()i razumjeti njihove različitosti, onda ste došli na pravo mjesto. Moćne su metode popisa koje ćete definitivno koristiti u svojim Python projektima.

U ovom ćete članku naučiti:

  • Kako i kada koristiti .append()metodu.
  • Kako i kada koristiti .extend()metodu.
  • Njihove glavne razlike.

Započnimo. ✨

? Dodati

Pogledajmo kako .append()metoda djeluje iza kulisa.

Koristite slučajeve

Ovu biste metodu trebali koristiti kada želite dodati jednu stavku na kraj popisa.

Ps Savjeti: Možete dodati stavke bilo koje vrste podataka jer popisi mogu sadržavati elemente različitih vrsta podataka.

Sintaksa i argumenti

Da biste pozvali .append()metodu, morat ćete upotrijebiti ovu sintaksu:

S lijeva na desno:

  • Popis koji će biti izmijenjen. To je obično varijabla koja upućuje na popis.
  • Točka, nakon koje slijedi naziv metode .append().
  • U zagradi, stavka koja će se dodati na kraj popisa.

? Savjeti: Točka je vrlo važna. To se naziva "točkovni zapis". Točka u osnovi kaže "pozovite ovu metodu na ovom određenom popisu", pa će se učinak metode primijeniti na popis koji se nalazi ispred točke.

Primjeri

Evo primjera kako koristiti .append():

# Define the list >>> nums = [1, 2, 3, 4] # Add the integer 5 to the end of the existing list >>> nums.append(5) # See the updated value of the list >>> nums [1, 2, 3, 4, 5]

? Savjeti: Kada koristite .append()izvorni popis modificiran. Metoda ne stvara kopiju popisa - mutira izvorni popis u memoriji.

Pretvarajmo se da provodimo istraživanje i da želimo analizirati podatke prikupljene pomoću Pythona. Moramo dodati novo mjerenje na postojeći popis vrijednosti.

Kako to radimo? Koristimo .append()metodu!

Možete ga vidjeti ovdje:

# Existing list >>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] # Add the float (decimal number) to the end of the existing list >>> nums.append(7.34) # See the updated value of the list >>> nums [5.6, 7.44, 6.75, 4.56, 2.3, 7.34]

Ekvivalentno ...

Ako ste upoznati s rezanjem niza, popisa ili nabora, ono što se .append()stvarno događa iza kulisa ekvivalentno je:

a[len(a):] = [x]

Ovim primjerom možete vidjeti da su ekvivalentni.

Korištenje .append():

>>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] >>> nums.append(4.52) >>> nums [5.6, 7.44, 6.75, 4.56, 2.3, 4.52]

Korištenje rezanja popisa:

>>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] >>> nums[len(nums):] = [4.52] >>> nums [5.6, 7.44, 6.75, 4.56, 2.3, 4.52]

Dodavanje niza

Što mislite o ovom primjeru? Što mislite da će se dobiti?

>>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] >>> nums.append([5.67, 7.67, 3.44]) >>> nums # OUTPUT?

Jesi li spreman? Ovo će biti rezultat:

[5.6, 7.44, 6.75, 4.56, 2.3, [5.67, 7.67, 3.44]]

Možda se pitate, zašto je cijeli popis dodan kao jedna stavka? To je zato što .append()metoda dodaje cijelu stavku na kraj popisa. Ako je stavka slijed poput popisa, rječnika ili nabora, cijeli će se slijed dodati kao jedna stavka postojećeg popisa.

Ovdje imamo još jedan primjer (dolje). U ovom slučaju, stavka je nabor i dodaje se kao jedna stavka popisa, a ne kao pojedinačne stavke:

>>> names = ["Lulu", "Nora", "Gino", "Bryan"] >>> names.append(("Emily", "John")) >>> names ['Lulu', 'Nora', 'Gino', 'Bryan', ('Emily', 'John')]

? Produžite

Sada zaronimo u funkcionalnost .extend()metode.

Koristite slučajeve

Ovu biste metodu trebali koristiti ako trebate dodati nekoliko stavki na popis kao zasebne stavke .

Let me illustrate the importance of this method with a familiar friend that you just learned: the .append() method. Based on what you've learned so far, if we wanted to add several individual items to a list using .append(), we would need to use .append() several times, like this:

# List that we want to modify >>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] # Appending the items >>> nums.append(2.3) >>> nums.append(9.6) >>> nums.append(4.564) >>> nums.append(7.56) # Updated list >>> nums [5.6, 7.44, 6.75, 4.56, 2.3, 2.3, 9.6, 4.564, 7.56]

I'm sure that you are probably thinking that this would not be very efficient, right? What if I need to add thousands or millions of values? I cannot write thousands or millions of lines for this simple task. That would take forever!

So let's see an alternative. We can store the values that we want to add in a separate list and then use a for loop to call .append() as many times as needed:

# List that we want to modify >>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] # Values that we want to add >>> new_values = [2.3, 9.6, 4.564, 7.56] # For loop that is going to append the value >>> for num in new_values: nums.append(num) # Updated value of the list >>> nums [5.6, 7.44, 6.75, 4.56, 2.3, 2.3, 9.6, 4.564, 7.56]

This is more efficient, right? We are only writing a few lines. But there is an even more efficient, readable, and compact way to achieve the same purpose: .extend()!

>>> nums = [5.6, 7.44, 6.75, 4.56, 2.3] >>> new_values = [2.3, 9.6, 4.564, 7.56] # This is where the magic occurs! No more for loops >>> nums.extend(new_values) # The list was updated with individual values >>> nums [5.6, 7.44, 6.75, 4.56, 2.3, 2.3, 9.6, 4.564, 7.56]

Let's see how this method works behind the scenes.

Syntax and Arguments

To call the .extend() method, you will need to use this syntax:

From Left to Right:

  • The list that will be modified. This is usually a variable that refers to the list.
  • A dot . (So far, everything is exactly the same as before).
  • The name of the method extend. (Now things start to change...).
  • Within parentheses, an iterable (list, tuple, dictionary, set, or string) that contains the items that will be added as individual elements of the list.

? Tips: According to the Python documentation, an iterable is defined as "an object capable of returning its members one at a time". Iterables can be used in a for loop and because they return their elements one at a time, we can "do something" with each one of them, one per iteration.

Behind the Scenes

Let's see how .extend() works behind the scenes. Here we have an example:

# List that will be modified >>> a = [1, 2, 3, 4] # Sequence of values that we want to add to the list a >>> b = [5, 6, 7] # Calling .extend() >>> a.extend(b) # See the updated list. Now the list a has the values 5, 6, and 7 >>> a [1, 2, 3, 4, 5, 6, 7]

You can think of .extend() as a method that appends the individual elements of the iterable in the same order as they appear.

In this case, we have a list a = [1, 2, 3, 4] as illustrated in the diagram below. We also have a list b = [5, 6, 7] that contains the sequence of values that we want to add. The method takes each element of b and appends it to list a in the same order.

After this process is completed, we have the updated list a and we can work with the values as individual elements of a.

? Tips: The list b used to extend list a remains intact after this process. You can work with it after the call to .extend(). Here is the proof:

>>> a = [1, 2, 3, 4] >>> b = [5, 6, 7] >>> a.extend(b) >>> a [1, 2, 3, 4, 5, 6, 7] # List b is intact! >>> b [5, 6, 7]

Examples

You may be curious to know how the .extend() method works when you pass different types of iterables. Let's see how in the following examples:

For tuples:

The process works exactly the same if you pass a tuple. The individual elements of the tuple are appended one by one in the order that they appear.

# List that will be extended >>> a = [1, 2, 3, 4] # Values that will be added (the iterable is a tuple!) >>> b = (1, 2, 3, 4) # Method call >>> a.extend(b) # The value of the list a was updated >>> a [1, 2, 3, 4, 1, 2, 3, 4]

For sets:

The same occurs if you pass a set. The elements of the set are appended one by one.

# List that will be extended >>> a = [1, 2, 3, 4] # Values that will be appended (the iterable is a set!) >>> c = {5, 6, 7} # Method call >>> a.extend(c) # The value of a was updated >>> a [1, 2, 3, 4, 5, 6, 7]

For strings:

Strings work a little bit different with the .extend() method. Each character of the string is considered an "item", so the characters are appended one by one in the order that they appear in the string.

# List that will be extended >>> a = ["a", "b", "c"] # String that will be used to extend the list >>> b = "Hello, World!" # Method call >>> a.extend(b) # The value of a was updated >>> a ['a', 'b', 'c', 'H', 'e', 'l', 'l', 'o', ',', ' ', 'W', 'o', 'r', 'l', 'd', '!']

For dictionaries:

Dictionaries have a particular behavior when you pass them as arguments to .extend(). In this case, the keys of the dictionary are appended one by one. The values of the corresponding key-value pairs are not appended.

In this example (below), the keys are "d", "e", and "f". These values are appended to the list a.

# List that will be extended >>> a = ["a", "b", "c"] # Dictionary that will be used to extend the list >>> b = {"d": 5, "e": 6, "f": 7} # Method call >>> a.extend(b) # The value of a was updated >>> a ['a', 'b', 'c', 'd', 'e', 'f']

Equivalent to...

What .extend() does is equivalent to a[len(a):] = iterable. Here we have an example to illustrate that they are equivalent:

Using .extend():

# List that will be extended >>> a = [1, 2, 3, 4] # Values that will be appended >>> b = (6, 7, 8) # Method call >>> a.extend(b) # The list was updated >>> a [1, 2, 3, 4, 6, 7, 8] 

Using list slicing:

# List that will be extended >>> a = [1, 2, 3, 4] # Values that will be appended >>> b = (6, 7, 8) # Assignment statement. Assign the iterable b as the final portion of the list a >>> a[len(a):] = b # The value of a was updated >>> a [1, 2, 3, 4, 6, 7, 8]

The result is the same, but using .extend() is much more readable and compact, right? Python truly offers amazing tools to improve our workflow.

? Summary of their Differences

Now that you know how to work with .append() and .extend(), let's see a summary of their key differences:

  • Effect: .append() adds a single element to the end of the list while .extend() can add multiple individual elements to the end of the list.
  • Argument: .append() takes a single element as argument while .extend() takes an iterable as argument (list, tuple, dictionaries, sets, strings).

I really hope that you liked my article and found it helpful. Now you can work with .append() and .extend() in your Python projects. Check out my online courses. Follow me on Twitter. ⭐️