Python class generator to list

kenichi-shibata / python-generators.md

You can convert a generator to a list however on the process it will lose its value and transfer it to the list.

 >> y = yrange(5) >>> ylist = list(y) >>> ylist [0, 1, 2, 3, 4] >>> ylist [0, 1, 2, 3, 4] >>> list(y) [] 

You may assign it to a variable to retain the list. Keep in mind it the original generator will be gone.

The power to send to generators

 >>> def whizbang(): for i in range(10): x = yield i print('i got <>'.format(x)) >>> bangbang = whizbang() >>> bangbang.__next__() 0 >>> next(bangbang) i got None 1 >>> bangbang.__next__() i got None 2 >>> next(bangbang) i got None 3 >>> bangbang.__next__() i got None 4 

next(generator) is the same as generator.next(). Similar to how vars(class) is the same as class.dict.

 >>> next(bangbang) i got None 5 

Let’s start sending stuff. Generators have generator.send() method.

 >>> bangbang.send('yo') i got yo 6 >>> bangbang.send('yo yo yo') i got yo yo yo 7 

In this case bangbang.send’s parameter is assigned to x. Since x = yield i, means x = yield send value and yield i

 >>> list(bangbang) i got None i got None i got None [8, 9] 

converting to list is not going to work with .send()

 >>> bangbang = whizbang() >>> next(bangbang) 0 >>> list(bangbang.send('test')) i got test Exception: TypeError: 'int' object is not iterable --------------------------------------------------------------------------- TypeError Traceback (most recent call last) in () ----> 1 list(bangbang.send('test')) TypeError: 'int' object is not iterable>>> 

you will need to call next(generator) at least once before doing a generator.send()

 >>> bangbang = whizbang() >>> bangbang.send('s') Exception: TypeError: can't send non-None value to a just-started generator --------------------------------------------------------------------------- TypeError Traceback (most recent call last) in () ----> 1 bangbang.send('s') TypeError: can't send non-None value to a just-started generator 

Removing values on generator early

Cleaning the values inside a generator is useful. For example if you application run into unknownerror and that left your application on a dirty state instead of risk writing a wrong data you can just close the generator early.

 >>> bangbang = whizbang() >>> bangbang >>> bangbang.__next__ >>> bangbang.__next__() 0 >>> bangbang.__next__() i got None 1>>> bangbang.__next__() i got None 2>>> bangbang.__next__() i got None 3>>> bangbang.__next__() i got None 4>>> bangbang.close() >>> bangbang.__next__() Exception: StopIteration: --------------------------------------------------------------------------- StopIteration Traceback (most recent call last) in () ----> 1 bangbang.__next__() StopIteration: 

As you see above bangbang should iterate until 10 however it stopped at 4 since we called bangbang.close()

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Convert Generator to List in Python

In Python, a list is iterable where every element gets stored at some specific index in a contiguous memory location. We can access the elements from their indexes.

Generator objects resemble iterators in Python but do not store elements in the memory. Both lists and generators represent a sequence of elements in Python. Let us understand more about generator objects in Python.

The return keyword is used to return some value from a function. The yield keyword in Python works similarly. It sends a value from the function to the caller and then resumes the function execution. Any function that has a yield keyword, is termed a generator function.

Using generators functions in Python, we can send a sequence of elements to the caller. These functions return a generator object which can be iterated over. We can iterate over the generator object using a for loop.

We can also use a generator expression to initiate a generator object. A generator expression is similar to list comprehension where we run a for loop in a single line of code to create a sequence.

The values from a generator can be stored in an actual data object. We can convert generator to list in Python.

Ways to convert generator to list in Python

We will now discuss how to convert generator to list in Python.

Using the list() function to convert generator to list in Python

The list() constructor is used to initiate list objects. We can pass a generator object to this function to convert generator to list in Python.

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Convert Generator To List In Python

Last updated June 5, 2023 by Jarvis Silva Looking for a tutorial on how to convert generator to list in python then you are at the right place, a generator is like a normal function but instead of using the return keyword a generator function uses a yield keyword, when a function uses yield keyword it is called as a generator below is an example.

 # Normal Function def normal_func(): return 1 # Generator def gen_func(): yield 1 

When we print the generator function it returns a generator object, so our goal is to convert the generator function into a list, The list will contain all the yield values of the generator.

Convert Generator To List In Python Code

 def nums_gen(): yield 1 yield 2 yield 3 yield 4 yield 5 # prints a generator object print(nums_gen()) # converting generator to list using list() nums_gen = list(nums_gen()) # prints a list print(nums_gen) 

Above is the python program to convert a generator to list, the code defines a generator function that produces a sequence of numbers, we use the list() function to converted result of generator function to list the code gives below output.

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I hope you found what you were looking for from this python tutorial and if you want more python tutorials like this, do join our Telegram channel to get updated.

Thanks for reading, have a nice day 🙂

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Convert Generator Object to List in Python (3 Examples)

Hi! This tutorial will show you 3 ways to transform a generator object to a list in the Python programming language.

The table of content is structured as follows:

Let’s jump into the Python code!

Create Sample Generator Object

Here, we will create the sample generator object that will be changed into a Python list using tuple comprehension. Therefore, in your preferred Python IDE, run the line of code below to create the sample generator object:

gen_obj = (x for x in range(5)) print(type(gen_obj)) #

However, in each of the examples that follow, the generator object will need to be run first in order for it to be turned into a list of integers; otherwise, it will print out an empty list.

Example 1: Change Generator Object to List Using list() Constructor

In this first example, we will turn the generator object to a list using the list() constructor:

gen_obj = (x for x in range(5)) list_from_gen = list(gen_obj) print(list_from_gen) # [0, 1, 2, 3, 4] print(type(list_from_gen)) #

In the above code, the list() constructor changes the generator object into a list of integers, starting at 0.

Example 2: Change Generator Object to List Using extend() Method

In this next example, we will transform the generator object to a list using the extend() method:

gen_obj = (x for x in range(5)) list_from_gen = [] list_from_gen.extend(gen_obj) print(list_from_gen) # [0, 1, 2, 3, 4] print(type(list_from_gen)) #

In the above example, we first created an empty list with the square brackets [], and then we populated that empty list with the elements of the generator object using the extend() method.

Example 3: Change Generator Object to List Using List Comprehension

In this final example, we will change the generator object to a list using list comprehension like so:

gen_obj = (x for x in range(5)) list_from_gen = [x for x in gen_obj] print(list_from_gen) # [0, 1, 2, 3, 4] print(type(list_from_gen)) #

The list comprehension in the above example enabled us to iterate through the generator object and store its elements inside in a list.

With that, I hope you have learned how to convert a generator object to a list in Python. I hope you found this tutorial helpful!

Video, Further Resources & Summary

Do you need more explanations on how to convert a generator object to a list in Python? Then you should have a look at the following YouTube video of the Statistics Globe YouTube channel.

In the video, we explain in some more detail how to convert a generator object to a list in Python.

The YouTube video will be added soon.

Furthermore, I encourage you to check out other interesting Python list tutorials on Statistics Globe, starting with these ones:

This post has shown how to convert a generator object to a list in Python. In case you have further questions, you may leave a comment below.

This page was created in collaboration with Ifeanyi Idiaye. You might check out Ifeanyi’s personal author page to read more about his academic background and the other articles he has written for the Statistics Globe website.

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Python Generator — How to create or iterate a generator

The Python generator (expression) is declared on the fly as follows:

a = [1, 3, 5] g = (i * i for i in a) print(g) # at 0x11940ef90> for x in g: print(x) # 1 # 9 # 25 

Precisely, g is a generator expression called «generator», which is fuzzy and not the form or expression of a list-like object. g is a generator, not a list (nor list comprehension). A generator generates values in the for loop but doesn’t save those in memory. Meanwhile, all the elements of a list are saved in memory. Generator uses memory efficiently.

You can’t get each element a generator generates by an index.

a = [1, 3, 5] g = (i * i for i in a) print(g[0]) # TypeError: 'generator' object is not subscriptable 

You can iterate what a generator generates.

a = [2, 3, 4] g = (i + 100 for i in a) for x in g: print(x) # 102 # 103 # 104 

g = (i * i for i in range(6)) for x in g: print(x) # 0 # 1 # 4 # 9 # 16 # 25 

An empty list can be an «empty» generator.

a = [] g = (i * i for i in a) for x in g: print(x) # 

A generator generates values once

g = (i * i for i in range(6)) for v in g: print(v) print('***') for w in g: print(w) # 0 # 1 # 4 # 9 # 16 # 25 # *** 

v are iterated and the square numbers (0-25) are printed. But w in g isn’t iterated. The generator generates all values in the first loop. The next example shows a generator can stop generating in the loop and start again in the next loop.

g = (i * i for i in range(6)) j = 0 for v in g: j += 1 if j < 4: print(v) else: break print('***') for w in g: print(w) # 0 # 1 # 4 # *** # 16 # 25 

Generator and next

You can get the item of a generator expression using next() , which is a Python built-in function and returns "next value" of generator.

g = (i * i for i in range(6)) print(next(g)) # 0 print(next(g)) # 1 print(next(g)) # 4 print(next(g)) # 9 print(next(g)) # 16 print(next(g)) # 25 print(next(g)) # StopIteration 

First, next() returns 0 because it's the first time to generate i * i . 6th next() returns 25 but the next doesn't exist. So the last next() raises a StopIteration.

Convert a Python generator to a Python list or set

You can convert a Python generator to a list.

a = [1, 2, 3] g = (i * i for i in a) b = list(g) print(b) # [1, 4, 9] 

Also you can convert a generator to a set.

a = [1, 2, 3] g = (i * i for i in a) b = set(g) print(b) #

Length of generator

The len() can't take a Python generator.

g = (i * i for i in range(5)) c = len(g) # TypeError: object of type 'generator' has no len() 

So, to get the length of a generator, convert it to a list.

g = (i * i for i in range(5)) s = list(g) c = len(s) # TypeError: object of type 'generator' has no len() print(s) # [0, 1, 4, 9, 16] print(c) # 5 

Sum of values generated

g = (i * i for i in range(5)) m = sum(g) print(m) # 30 

The sum() sums all the elements generated. You don't need to convert a generator to a list to sum.

g = (i * i for i in range(5)) s = list(g) m = sum(s) 

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