How to Read a File and Then Put Into a List

Storing information in files lets you lot go on a record of the data with which a program is working. This ways you lot don't have to generate information over once again when working with a program. You just read that data from a file.

To read files, use the readlines() method. Once you've read a file, y'all use split() to plough those lines into a list.

In this guide, we discuss how to use the split up() method to read a text file into a list. We'll refer to an example so y'all tin can get started reading text files into lists chop-chop.

Python: Read Text File into List

Let's start with a text file chosen grilled_cheese.txt. This file contains the ingredients for a grilled cheese sandwich. Our file content looks like this:

two tbsp, ricotta ane tbsp, grated parmesan 50g, mozzarella 25g, gorgonzola two, thick slices white bread i tbsp, butter

The first cavalcade in our file contains the quantity of each ingredient to be used. The second column contains the name of an ingredient.

Nosotros read this file into our lawmaking using the open() and readlines() methods:

with open("grilled_cheese.txt", "r") as grilled_cheese: 	lines = grilled_cheese.readlines() 	print(lines)

In our code, nosotros open a file called "grilled_cheese.txt" in read mode. Read manner is denoted by the "r" character in our open up() statement. Next, we print those lines to the console.

Let'due south meet what our Python code returns:

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['2 tbsp, ricotta\n', 'ane tbsp, grated parmesan\n', '50g, mozzarella\north', '25g, gorgonzola\northward', '2, thick slices white bread\n', '1 tbsp, butter\n']

Our code returns a list of each line in our file. This is not quite the output we are expecting. While nosotros've read our file into a list, we take a trouble: each line is stored in its own string. Ingredients and their quantities are not separate.

Divide Values into a Listing

To solve this problem, we use the split() method. This method lets usa divide a cord using a separator character we specify.

To kickoff, we declare two lists: quantities and ingredients. This code will remain indented considering it is part of our open() block of code.

            quantities = [] 	ingredients = []

Nosotros'll iterate over our list so nosotros tin can admission each line of text from our file. Then we'll split each line into two parts. The dividing bespeak is the comma followed by a space on each line:

for fifty in lines: 		 as_list = l.split(", ") 		 quantities.append(as_list[0]) 		 ingredients.append(as_list[i])

The for loop lets us read our file line by line. The first value in "as_list" is the quantity of an ingredient. The second value is the proper name of the ingredient. We then impress both of these lists to the console:

            impress(quantities) 	print(ingredients)

Let's run our code:

['ii tbsp, ricotta\northward', '1 tbsp, grated parmesan\northward', '50g, mozzarella\n', '25g, gorgonzola\northward', 'ii, thick slices white bread\due north', '1 tbsp, butter\north'] ['ii tbsp', '1 tbsp', '50g', '25g', 'two', '1 tbsp'] ['ricotta\northward', 'grated parmesan\n', 'mozzarella\n', 'gorgonzola\north', 'thick slices white bread\n', 'butter\n']

Our lawmaking prints 3 lists to the console. The first list is a list of all the lines of text in our file. The second list contains all the quantities from our file. The third list contains all the ingredients.

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Remove New Lines

There is still one improvement that we need to make. Every ingredient ends in the "\n" graphic symbol. This grapheme denotes a new line. We can remove this character by using the supercede() method:

for l in lines: 	   	  as_list = l.split(", ") 		  quantities.append(as_list[0]) 		  ingredients.suspend(as_list[1].supplant("\northward", ""))

In our for loop, we replace the value "\n" with an empty string. Nosotros practice this on the as_list[1] value which correlates to the name of each ingredient.

Now that we've made this change, our plan is set up:

with open("grilled_cheese.txt", "r") as grilled_cheese: 	   lines = grilled_cheese.readlines()  	   quantities = [] 	   ingredients = []  	   for l in lines: 	  			 as_list = l.split(", ") 			     quantities.suspend(as_list[0]) 			     ingredients.append(as_list[one].supervene upon("\n", ""))  	   print(quantities) 	   print(ingredients)

Let's run our code and see what happens:

['2 tbsp', '1 tbsp', '50g', '25g', '2', 'i tbsp'] ['ricotta', 'grated parmesan', 'mozzarella', 'gorgonzola', 'thick slices white breadstuff', 'butter']

Our code successfully transforms our text file into 2 lists. One list contains the quantities of ingredients for a recipe. The other list contains the ingredients we'll use for the recipe.

Determination

You tin can read a text file using the open up() and readlines() methods. To read a text file into a list, use the separate() method. This method splits strings into a list at a sure grapheme.

In the example above, nosotros carve up a string into a list based on the position of a comma and a space (", "). Now you're set to read a text file into a list in Python similar an expert.

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Source: https://careerkarma.com/blog/python-read-text-file-into-list/

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