Finding the First Match From a Python Iterable

Key Takeaways

getting the first match from our python list all iterable at some point in your python Journey you may need to find a first item that matches a certain Criterion in a python iterable such as a list or dictionary the simplest case is that you need to confirm that a particular item exists in the iterable for example you may want to find a name in a list of names or a substring inside a string in these cases you're best off using the in operator however there are many use cases when you may want to look for items with specific properties for instance you may need to find a non-zero value in a list of numbers find a name of a particular length in a list of strings or find a modified dictionary in a list of dictionaries based on a certain attribute this course will cover how to best approach all three scenarios one option is to transform your whole iterable to a new list and then use index to find the first item matching your Criterion here you've used index to find that Tiffany is the first name in your list with seven characters this solution isn't great partly because you calculate the Criterion for all elements even if the first item is a match in these situations you're searching for a calculated property of the items you're iterating over in this course you'll learn how to match such a derived attribute without needing to do unnecessary calculations any code you see entered in a raffle will be using the enhanced raffle B python it offers a number of enhancements over the standard raffle including code highlighting and suggestions so now you know what's going to be covered let's get started how to get the first matching item in a python list you may already know about the in Python operator which can tell you if an item is in an iterable while this is the most efficient method that you can use for this purpose sometimes you may need to match based on a calculated property of the items such as their lengths for example you might be working with a list of dictionaries typical of what you might get when processing Json data on screen you'll see some country data from the country Json repository being saved as a dictionary in a python file this will allow the data to be imported quickly across multiple raffle sessions saving you time if you tackle this course across multiple settings you might want to grab the first dictionary that has a population of over 100 million the in operator isn't a great choice for two reasons first you'd need to have the full dictionary to match it and secondly it wouldn't return the actual object but a Boolean value there's no way to use in if you need to find a dictionary based on an attribute of it such as population the most readable way to find and manipulate the first element in the list based on a calculated value is to use the humble for Loop instead of printing the target object you can do anything you like with it in the for Loop body after you're done be sure to break the for Loop so that you don't needlessly search the rest of the list note that using the break statement applies if you're looking for the first match from the iterable if you're looking to get or process all of the matches then you can do without the break the for Loop approach is the one taken by the first package which is a tiny package you can download from Pi Pi that exposes a general purpose function first this function Returns the first truthy value from an iterable by default with an optional key parameter to return the first truthy value after it's been passed through the key argument note that on Python 3.10 and later you can use structural pattern matching to match these kinds of data structures in a way that you may prefer on screen you'll see how you can use this technique to match a country with a population of more than 100 million here you use a guard to only match certain populations using structural pattern matching instead of regular conditional statements can be more readable and concise if the matching patterns are complex enough later in the course you'll Implement your own variation of the first function but next you'll look into another way of returning a first match using generators using python generators to get the first match python generator iterators are memory efficient iterables that can be used to find the first element in a list or any iterable they're a core feature of python being used extensively under the hood it's likely you've already used generators without even knowing it the potential issue with generators is that they're a bit more abstract and as such not quite as readable as for loops you do get some performance benefits from generators but these are often negligible when the importance of readability is taken into consideration that said using them can be fun and level up your python game in Python you can make a generator in various ways but in this course you'll be working with generator comprehensions once you've defined a generator iterator you can then call the next function with the generator as an argument producing the countries one by one until the country's list is exhausted to find the first element matching a certain criteria in a list you can add a conditional expression to the generator comprehension so the resulting iterator will only yield items that match the criteria in the example seen on screen you use a conditional expression to generate items based on whether the population attribute is over 100 million so now the generator will only produce dictionaries with a population attribute of over 100 million this means that the first time you call next with the generator iterator it will yield the first element that you're looking for in the list just like the for Loop version note that you'll get an exception if you call next and there's no match or the generator is exhausted to prevent this you can pass in a default argument to next monster generator is finished producing matches it will return the default value that's been passed in since you're returning none you get no output in the rebel if you hadn't passed in the default value you would get a stop iteration exception in terms of readability a generator isn't quite as natural as a for Loop so why would you use one for this purpose well in the next section of the course you'll be doing a quick performance comparison to find out