from itertools import izip as zip So that is still: (can't find the original thread on Google at the moment)? Unnecessary use of a comprehension Instead of using an identitiy comprehension, consider using the list, dict or … So, avoid that global keyword as much as you can. Oct 26, 2010 at 9:31 am: recently wrote a article based on a debate here. In Python 2, zip returns a list, to avoid creating an unnecessary list, use izip instead (aliased to zip can reduce code changes when you move to Python 3). We’ve already seen an example of how we might use list comprehension to filter the results of one list into a new list. Yes list comprehension are faster than ordinary loop,but dont do to much Premature optimization. Now let’s look at how we might use it to generate a list of data. Also, Python is faster retrieving a local variable than a global one. For starters, with list comprehension we don't need to initialize an empty list, i.e. 10. we don't need the statement highest_paid_actors_birthyear=[]. Within 30 minutes, I had flexible, reusable code which later saved me hours of unnecessary manual labor! Xah Lee. When would I use a comprehension? These Python interview questions will challenge your algorithmic thinking skills as well as your Python programming skills. What did work in Python 2 and doesn't work in 3, is using a list comprehension like all([x < limit for x in items]) This is because list comprehensions are now implemented with their own function object like generator expressions have always been. Instead of using list/dict/set around a generator expression, they can be written as their respective comprehension… In Python, you can concatenate strings using “+”. The idiomatic way to perform an explicit typecheck in Python is to use isinstance(x, Y) rather than type(x) == Y, type(x) is Y. Unnecessary use of generators. Be careful not to create new iterables when you don’t need to: if you’re only going to loop over an iterable once, just use the iterable you already have. Now let’s look at how we might use it to generate a list of data. Seven Clean Steps To Reshape Your Data With Pandas Or How I Use Python Where Excel Fails Concepts: multi-level indexing, pivoting, stacking, apply, lambda, list-comprehension 15 November 2017 A few weeks ago, a colleague sent me a spreadsheet with data on a public health intevention, consisting of many tabs, one tab per organization. ... unnecessary, confusing, etc. [Python] is list comprehension necessary? In order for my code to be efficient, loops need to be terminated prematurely to prevent unnecessary iterations. This actually does not work in Python 2 either. In Python, we often care less about whether something is a list and more about whether it’s an iterable. 3. Use join() to concatenate strings. In a previous post, we looked at how we could use python to determine the compound interest on a loan. One of the frequently repeated mantras I hear from Python veterans is, "Premature optimization is the root of all evil" Using append() to tell Python that each new element should be added to the end is also unnecessary; we don't need to use append() in list comprehension. Seven Clean Steps To Reshape Your Data With Pandas Or How I Use Python Where Excel Fails ... but I decided to use Python’s Pandas library to automate this task so I set to work developing the script. In a previous post, we looked at how we could use python to determine the compound interest on a loan. ?What's List Comprehension and Why is it Harmful?? It is unnecessary to use a generator expression within a call to list, dict or set since there are comprehensions for each of these types. Eventually, I came to be comfortable with them and use them often. We’ve already seen an example of how we might use list comprehension to filter the results of one list into a new list. So when would you actually use a comprehension? Using few global variables is an effective design pattern because it helps you keep track of scope and unnecessary memory usage.