What is Python File Reading?
Reading and writing files is an incredibly important skill since more often than not developers need to work with files of different formats when developing programs.
Text files, CSV files and JSON files are the most common types of files used in Python programs. Both JSON and CSV files require importing extra modules, unlike text files that we can just import in and out.
Having the files that we need to work within the same directory with the Python file that we are writing code allows us to reference them directly.
Managing files in Python can be a daunting task especially if we have to open and close the files manually. However, python provides us with the context manager that gives developers flexibility when managing resources in Python.
How to use Python File Reader methods?
There are two keywords that are important when working with the context manager, the keyword ‘with’ and ‘open(…)’. Now inside the parentheses that precede the word open(…), we’re going to give it the name of the file and how we want to open the file.
There are four different modes of opening files in python, we can open or read or write in bytes representation as enlisted below.
- “r” – Read – Open a file for reading (Default).
- “a” – Append – Opens a file for appending.
- “w” – Write – Opens a file for writing.
- “x” – Create – Creates the specified file.
In this case, we’re going to be using just reading. So inside our with open() statement here we will have quotes marks and then we type the name of the file.
Once we pass the name of the file that we intend to open which in this case is called ‘mytextfile.txt.’ we need to put a comma and then another quote mark and the ‘r’ for reading.
Now because we’re using the context manager then we need to give it a variable so that it’s going to open it as this variable. We can use ‘f’ which is the default value.
If we hit enter and move to the next indented line we will still be within the context manager, and in order to read the contents of the file, we need to do print(f.read).
Alternatively, we could save f.read into a variable and then print it outside the context manager instead, since the information will still be saved.
How to read CSV files with the Python File Reader?
Opening text files is useful but nowhere near as useful as opening CSV files. A CSV file is opened in a similar way, however, we need to import the CSV module first before we can start using CSV files.
The CSV module is in the standard library and therefore all that we need to do is import CSV. Then we’re going to do with open() in the same way as we did before and then pass in the name of the CSV file which is ‘csvinfo.csv’, and again, we’re going to be doing ‘r’ for read-only and again as f.
We need to again create a variable that is going to represent our CSV reader we are just going to call this one reader is equal to csv.reader(). Now, if we try to print out this reader object is going to tell us that this is a reader object.
Now we can actually start to work with the file. A CSV file generally has rows so we’re going to do for row in the reader and we’re going to do a simple for loop through each one of those.
Once we print out the rows Python will turn each of the rows into a list that we have access to. The first row is made up of the row header followed by the rows that hold the data underneath.
How to read JSON files with Python File Reader
JSON file formats are also very common in programming. In order to work with JSON files in Python, we need to import the JSON library.
In a similar manner reading a JSON file begins by stating the two keywords with open(), before passing in the name of the JSON file that we intend to import which is ‘somejsondata.json’ and the state that we intend to access it i.e in the read-only mode we use ‘r’.
And now we need to use the JSON module that we have imported to load the JSON data into something that we can work with.
By stating as f at the end of the above statement we imply that we intend to store the file output as a variable, therefore we can create a variable ‘data’ and let it be equal to json.load(…).
Basically, this reads the JSON file from a text and thus we are also going to pass in the keyword ‘f’ within the parentheses.
Once we are done importing the JSON file we can now move the cursor to the outside of the context manager and print the variable data that now store the JSON file that we have loaded to the screen.
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