Files

Python allows you to work with the file system, which includes both files and directories. Using the built-in system functions, you can access, manipulate, open, read, write, append, and close files.

Opening a File

In Python, you can open a file using the built-in open function. This function accepts two required arguments: the name of the file you want to open and the mode in which you want to open it.

Here's an example:

file = open("example.txt", "r")

In the above code, "example.txt" is the name of the file you want to open and "r" is the mode. The mode "r" stands for "read" and it opens the file for reading. There are several other modes you can use:

"r": Read mode (default) - used for reading the contents of an existing file "w": Write mode - used for creating a new file or overwriting an existing file
"a": Append mode - used for appending data to an existing file
"x": Exclusive creation mode - used for creating a new file, but will raise an error if the file already exists
"b": Binary mode - used for reading or writing binary data You can combine the modes with "b" to open a file in binary mode.

For example, "rb" means to open the file in binary read mode, and "wb" means to open the file in binary write mode.

Reading a File

Here's an example of how you can read the contents of a file:


file = open("example.txt", "r")
contents = file.read()
print(contents)
file.close()

In this example, the read method is used to read the contents of the file, and then the close method is used to close the file after you're done with it. It's a good idea to always close your files when you're done with them, to ensure that the resources they use are properly released.

You can also use the with statement to automatically close the file for you, like this:

with open("example.txt", "r") as file:
    contents = file.read()
    print(contents)

In this example, the file is automatically closed after the with block is exited, even if an exception is raised.

Read File Line by Line

Maybe instead of getting the entire file, you want to read it line by line. Thankfully, there is already a built-in function for this. The readline() function reads a file line by line each time. If you use it twice, the second time will return the second line.

file = open("file.txt", "r")
print(file.readline())
print(file.readline())

Hello!
Welcome to StackTips!

Alternatively, you can just loop over the lines, like so:

file = open("file.txt", "r")
for line in file:
    print(line)

Hello!
Welcome to StackTips!
Have fun!

Closing a File

Closing a file is important because it is sometimes needed to ensure any changes to a file are propagated in the file system.

This is how to close a file once you're finished with it:

file = open("file.txt", "r")
for line in file:
    print(line)
file.close()

Our file is now closed!

Appending to Existing File

You can append text to an existing file pretty easily. Simply switch the mode when you open and use the write() function:

file = open("file.txt", "a")
file.write("Coding is fun!")
file.close()

file = open("file.txt", "r")
print(file.read())

Hello!
Welcome to StackTips!
Have fun!
Coding is fun!

Overwriting an Existing File

The only difference between appending and overwriting an existing file is the mode. Here is how you overwrite a file entirely:

file = open("file.txt", "w")
file.write("Coding is fun!")
file.close()

file = open("file.txt", "r")
print(file.read())

Coding is fun!

Creating new Empty Files

You can create a brand new file without any content in it by changing the mode to x:

file = open("file.txt", "x")
file.close()

A new blank file has been created!

Renaming a File

To rename a file using Python, we must import the os module, then use its rename() function.

Here's how that looks:

import os
os.rename("old_name.txt", "new_name.txt")

Pretty simple!

Deleting a File

Deleting a file also requires the use of the os module.

Here's how you do it:

import os

os.remove("file.txt")

Check if a File Exists

To avoid an error with trying to remove a file that does not exist, you should check if the file exists before trying to remove it.

This is how you do it:

import os

path = "file.txt"

if os.path.exists(path):
    os.remove(path)
else:
    print("This path does not exist: " + path)

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