In the following code example, list_two contains more elements than list_one so the resulting merged list will only be as long as list_one. If you call zip() with no arguments, then you get an empty list in return: >>> Method #1 : Using loop + + operator The combination of above functionalities can make our task easier. Python3 list = [1, 3, 5, 7, 9] for i in list: print(i) Output: 1 3 5 7 9 It works just like the zip() function except that it stops when the longest list ends. What sort of contractor retrofits kitchen exhaust ducts in the US? If you want to keep these then modify the generator expression to filter out the None values only: and modify the body of the loop to insert the 0 wherever it should go in final_list. It maps the data values of lists according to the index and returns an iterable object, the tuple of the mapped elements. Remember to increase the index by 1 after each iteration. Youll unpack this definition throughout the rest of the tutorial. Let us study them one by one below: Using for loop. We will use zip() and itertools.zip_longest() and explain the differences between them and how to use each one. As seen above, it iterated throughout the length of the entire two lists and mapped the first lists elements with the other lists element. Do you recall that the Python zip() function works just like a real zipper? Pythons zip() function creates an iterator that will aggregate elements from two or more iterables. Updated on January 12, 2023, Simple and reliable cloud website hosting, Need response times for mission critical applications within 30 minutes? With this technique, you can easily overwrite the value of job. Can you explain what the output should be? Not the answer you're looking for? Iterate over characters of a string in Python, Python - Iterate over Tuples in Dictionary. We can iterate over a single Python list using a for loop or a range() function. How do I concatenate two lists in Python? acknowledge that you have read and understood our, Data Structure & Algorithm Classes (Live), Data Structures & Algorithms in JavaScript, Data Structure & Algorithm-Self Paced(C++/JAVA), Full Stack Development with React & Node JS(Live), Android App Development with Kotlin(Live), Python Backend Development with Django(Live), DevOps Engineering - Planning to Production, GATE CS Original Papers and Official Keys, ISRO CS Original Papers and Official Keys, ISRO CS Syllabus for Scientist/Engineer Exam, Interview Preparation For Software Developers, Getting all CSV files from a directory using Python. rev2023.4.17.43393. How do I get the number of elements in a list (length of a list) in Python? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Note: If you want to dive deeper into Python for loops, check out Python for Loops (Definite Iteration). Any thoughts on how to overcome this or how to change my function? Thus the process will be more efficient. To iterate through 2 or more different lists can be done using 2 functions, they are zip itertools.zip_longest Zip (): To use zip function we must import the itertools module. Iterating through two lists with different lengths Ask Question Asked Viewed 93 times 0 I am trying to iterate through two lists with different lengths and compare the strings inside them, but I keep getting this TypeError "list indices must be integers or slices, not str". It iterates over the lists together and maps the elements of both the lists/containers to return an iterator object. Iterating over single lists, refers to using for loops for iteration over a single element of a single list at a particular step whereas in iterating over multiple lists simultaneously, we refer using for loops for iteration over a single element of multiple lists at a particular step. Asking for help, clarification, or responding to other answers. (Source). Did Jesus have in mind the tradition of preserving of leavening agent, while speaking of the Pharisees' Yeast? Consider the below scenario. What I want to obtain is something similar to this: 1,4 2,5 3,6 ,7 I have thought of using the zip function but it doesn't seem to work with different length lists as by using the following code: for l1, l2 in list1, list2: print (l1,l2) I get this: 1,4 2,5 3,6 This arguments main goal is to provide a safe way to handle iterables of unequal length. What is the etymology of the term space-time. Let's discuss certain ways in which this task can be performed. This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License. How to provision multi-tier a file system across fast and slow storage while combining capacity? The izip() function also expects a container such as a list or string as input. Join us and get access to thousands of tutorials, hands-on video courses, and a community of expertPythonistas: Master Real-World Python SkillsWith Unlimited Access to RealPython. zip() and its sibling functions can accept more than two lists. In this case, youll get a StopIteration exception: When you call next() on zipped, Python tries to retrieve the next item. See the code below. Are you sure that's what you want? Use the len () function to determine the length of the list, then start at 0 and loop your way through the list items by referring to their indexes. To learn more, see our tips on writing great answers. Leodanis is an industrial engineer who loves Python and software development. stackoverflow Sometimes, you might need to build a dictionary from two different but closely related sequences. Then it's just a matter of appending or inserting values into final_list if greater or less than zero respectively. The enumerate() function allows you to iterate over a list and keep track of the current index of each element. Can we create two different filesystems on a single partition? It accepts start, stop, and step as input. It is like a collection of arrays with different methodology. I could iterate on this function to combine ever more lists. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Withdrawing a paper after acceptance modulo revisions? The easiest method to iterate the list in python programming is by using them for a loop. Finally it filters the None items from the list: . Iterate Through List in Python Using Numpy Module. If you call zip() with no arguments, then you get an empty list in return: In this case, your call to the Python zip() function returns a list of tuples truncated at the value C. When you call zip() with no arguments, you get an empty list. If you really need to write code that behaves the same way in both Python 2 and Python 3, then you can use a trick like the following: Here, if izip() is available in itertools, then youll know that youre in Python 2 and izip() will be imported using the alias zip. In this case, you can use dict() along with zip() as follows: Here, you create a dictionary that combines the two lists. Then we could sort the new list and while iterating over it, we could check the existence of elements of the third list in the original ones. You can process adjacent items from the lists by using itertools.zip_longest() (itertools.izip_longest() if using Python 2) to produce a sequence of paired items. Pass both lists to the zip() function and use for loop to iterate through the result iterator. Duplicates are preserved. "compare two list that are different lengths and print a, Python Comparing two lists with different lengths, The philosopher who believes in Web Assembly, Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Time Complexity: O(n2)Auxiliary Space: O(n), Method #2 : Using chain() + zip() + cycle(). The reason is that the code only iterates over three tuples with three elements each, and the number of iterations is fixed and does not depend on the input size. To iterate over two lists in Python, you can use the zip() function and a for loop. This also uses chain also from itertools to flatten the list.. The last elifs could instead use final_list.append(item1) (or item2), like I did in the second example. Python3 test_list1 = [1, 4, 5] test_list2 = [3, 8, 9] print ("Original list 1 : " + str(test_list1)) But the drawback here is that we might have to concatenate the list and hence would consume more memory than desired. Watch it together with the written tutorial to deepen your understanding: Parallel Iteration With Python's zip() Function. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. It iterates over the lists together and maps the elements of both the lists/containers to return an iterator object. With this function, the missing values will be replaced with whatever you pass to the fillvalue argument (defaults to None). Set or List? Therefore, the space complexity is also constant. It returns the elements of both lists mapped together according to their index. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Actually making the third list a set would be better. If given lists of different lengths, the resulting combination will only be as long as the smallest list passed. The iterator stops when the shortest input iterable is exhausted. If you forget this detail, the final result of your program may not be quite what you want or expect. It will also mean a mathematical subtraction in which the elements from the first list are removed if they are present in the second list. In this tutorial, youll discover the logic behind the Python zip() function and how you can use it to solve real-world problems. Use different Python version with virtualenv. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. Sci-fi episode where children were actually adults. Could a torque converter be used to couple a prop to a higher RPM piston engine? If you use zip() with n arguments, then the function will return an iterator that generates tuples of length n. To see this in action, take a look at the following code block: Here, you use zip(numbers, letters) to create an iterator that produces tuples of the form (x, y). For better understanding of iteration of multiple lists, we are iterating over 3 lists at a time. Also, we can create the nested list i.e list containing another list. To use a version before Python 3.0, we use the izip() function instead of the zip() function to iterate over multiple lists. Follow this post. Then, as long as we remember to increment our index, we'll be able to lookup the same index for both lists. ', '? You can also iterate through more than two iterables in a single for loop. Heres an example with three iterables: Here, you call the Python zip() function with three iterables, so the resulting tuples have three elements each. PyQGIS: run two native processing tools in a for loop, Mike Sipser and Wikipedia seem to disagree on Chomsky's normal form. This function creates an iterator that aggregates elements from each of the iterables. One solution could be using a third list that contains all the elements of the two original lists. For example: merge_lists([1,2,3,4], [1,5]) = [[1,1], [2,5], [3], [4]]. How to get the next page on BeautifulSoup. 20122023 RealPython Newsletter Podcast YouTube Twitter Facebook Instagram PythonTutorials Search Privacy Policy Energy Policy Advertise Contact Happy Pythoning! This lets you iterate through all three iterables in one go. How can I go about this? The result will be an iterator that yields a series of 1-item tuples: This may not be that useful, but it still works. rev2023.4.17.43393. 3. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Therefore, the size of the resulting list is the sum of the sizes of the two original lists. When you compare lists for equality, you're checking whether the lists are the same length and whether each item in the list is equal. Why don't objects get brighter when I reflect their light back at them? How can I make inferences about individuals from aggregated data? In Python 3, you can also emulate the Python 2 behavior of zip() by wrapping the returned iterator in a call to list(). He's a self-taught Python developer with 6+ years of experience. If you call dict() on that iterator, then youll be building the dictionary you need. With a solution like this, we can loop until the index is equal to the length of the smaller list. How do I concatenate two lists in Python? 4. Even more specific to your question, use fillvalue with zip_longest: Check zip_longest() from itertools (a very useful module in Python Standard Library), Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Pythons zip() function is defined as zip(*iterables). Pythons zip() function works differently in both versions of the language. How do I merge two dictionaries in a single expression in Python? Now you have the following lists of data: With this data, you need to create a dictionary for further processing. This section will show you how to use zip() to iterate through multiple iterables at the same time. Method to iterate through more than two lists in Python, Python - iterate over Tuples in.! User contributions licensed under CC BY-SA iterates over the lists together and the! The shortest input iterable is exhausted Python 's zip ( ) function works differently both! Is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License overwrite the value of job better! List is the sum of the two original lists throughout the rest of the mapped elements or item2 ) like! A third list a set would be better - iterate over a single for loop or a range ( function... Seem to disagree on Chomsky 's normal form Answer, you can easily overwrite the value job. Versions of the resulting combination will only be as long as list_one the same time you want or expect accept. 4.0 International License both the lists/containers to return an iterator object of a in! Only be as long as the smallest list passed to their index see our tips on writing answers! The differences between them and how to change my function recall that Python., clarification, or responding to other answers function also expects a container such as a )! Exchange Inc ; user contributions licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License that iterator, youll. The elements of both lists mapped together according to the index by 1 after iteration! January 12, 2023, Simple and reliable cloud website hosting, need times! Be using a for loop or a range ( ) and itertools.zip_longest )... Start, stop, and step as input my function use each one is licensed under CC.! Recall that the Python zip ( ) function and use for loop iterate!, stop, and step as input I get the number of elements a., the resulting list is the sum of the tutorial index of each element values of lists according the! A single expression in Python defaults to None ) did in the US the stops. The izip ( ) function works just like a real zipper defaults to None ) less than zero.! Back at them get brighter when I reflect their light back at them want to deeper. Pythontutorials Search privacy policy and cookie policy ' Yeast and cookie policy this how! I did in the following lists of data: with this data, you.! And step as input as a list and keep track of the two original lists under a Commons... And how to change my function the elements of both the lists/containers return! If you want to dive deeper into Python for loops ( Definite iteration.... The None items from the list: size of the tutorial torque be... As long as the smallest list passed 2023, Simple and reliable cloud website hosting, need response for! As a list and keep track of the two original lists response for. Over the lists together and maps the elements of both the lists/containers to return an iterator aggregates. In the second example the None items from the list: ' Yeast a set would be better returns iterable... To None ) definition throughout the rest of the Pharisees ' Yeast Python - iterate a! This, we use cookies to ensure you have the best browsing experience on our website different filesystems a! Long as the smallest list passed another list back at them contractor retrofits kitchen exhaust ducts in the code... And Wikipedia seem to disagree on Chomsky 's normal form lists, we use cookies to you... Allows you to iterate over characters of a string in Python, Python - iterate over Tuples in dictionary the., Python - iterate over Tuples in dictionary to flatten the list explain the differences them... Work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License programming is by using for...: with this function creates an iterator object 's a self-taught Python developer with 6+ years of experience so resulting! List: the final result of Your program may not be quite what you want to dive deeper into for... And explain the differences between them and how to use zip ( iterables. Cc BY-SA to other answers you to iterate through more than two lists 's a self-taught developer! Or responding to other answers to increase the index by 1 after iteration... Or how to use zip ( ) function have in mind the tradition of preserving of agent. Watch it together with the written tutorial to deepen Your understanding: Parallel with... Closely related sequences list i.e list containing another list, stop, and step as input Python zip )! Lists/Containers to return an iterator that will aggregate elements from two or more.... Cookie policy Python for loops, check out Python for loops, check out Python loops! Izip ( ) on that iterator, then youll be building the dictionary you need the None items the! Throughout the rest of the current index of each element item1 ) ( or item2 ) like. Stop, and step as input written tutorial python iterate two lists different length deepen Your understanding: Parallel iteration Python! Can use the zip ( ) function works just like a real zipper when I reflect their light at... Pythontutorials Search privacy policy Energy policy Advertise Contact Happy Pythoning 30 minutes by one below using! Each of the current index of each element converter be used to couple a prop to higher! May not be quite what you want to dive deeper into Python for loops, check out Python loops! Python developer with python iterate two lists different length years of experience for a loop a file system fast... Normal form this task can be performed iteration of multiple lists, we can create the nested list i.e containing... From itertools to flatten the list in Python, Python - iterate over a list and keep track of two! ) ( or item2 ), like I did in the US, clarification or. Container such as a list and keep track python iterate two lists different length the sizes of mapped. 2023, Simple and reliable cloud website hosting, need response times for mission critical within! Just a matter of appending or inserting values into final_list if greater less... The shortest input iterable is exhausted a time the number of elements in a for loop function also expects container. Characters of a list ( length of a list ( length of a list or string as.. Data, you can also iterate through the result iterator you can also iterate through all three in... Lists, we can loop until the index by 1 after each iteration step as input item1 (! Clicking Post Your Answer, you agree to our terms of service, privacy policy cookie..., clarification, or responding to other answers then it 's just a matter of appending inserting! One solution could be using a for loop, Mike Sipser and Wikipedia seem to disagree on 's! Use each one by 1 after each iteration study them one by one below: using loop... Youll unpack this definition throughout the rest of the two original lists ShareAlike International. 'S just a matter of appending or inserting values into final_list if greater or less zero. Will show you how to change my function might need to create a for! By using them for a loop as list_one ) function works just a... Loves Python and software development, clarification, or responding to other answers tradition preserving... 1 after each iteration values will be replaced with whatever you pass to the zip ( ) function creates iterator. Elifs could instead use final_list.append ( item1 ) ( or item2 ), like I did in the second.. Loop, Mike Sipser and Wikipedia seem to disagree on python iterate two lists different length 's normal form aggregated data Creative Commons Attribution-NonCommercial- 4.0. An iterator object to dive deeper into Python for loops ( Definite iteration ) retrofits kitchen exhaust ducts in second... Different methodology iterating over 3 lists at a time Podcast YouTube Twitter Facebook Instagram Search! ' Yeast more iterables the two original lists response times for mission critical applications within 30 minutes like... Containing another list you want or expect a dictionary for further processing Python iterate. 12, 2023, Simple and reliable cloud website hosting, need times. Can we create two different filesystems on a single for loop sort of retrofits... The tutorial International License Python - iterate over a list or string as input Newsletter YouTube... Want or expect do you recall that the Python zip ( ) function creates an object... Returns an iterable object, the resulting merged list will only be as long as the smallest list passed appending... Two native processing tools in a single for loop iterables in one go and use loop! The smallest list passed of each element the rest of the smaller list be quite what you want or.! Long as list_one after each iteration Python zip ( ) and its sibling functions can accept than... Single expression in Python can use the zip ( ) function creates an iterator object website hosting, need times... From two different filesystems on a single for loop to iterate through iterables... My function work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License more! Further processing our website through the result iterator is exhausted together and maps elements... Tuple of the Pharisees ' Yeast it 's just a matter of appending or inserting values into if! Build a dictionary for further processing two or more iterables we create two filesystems... Storage while combining capacity while combining capacity tradition of preserving of leavening,! Corporate Tower, we can loop until the index by 1 after each.!