Industrial Training




Reading And Writing Files


Open a File on the Server


Assume we have the following file, located in the same folder as Python:


demofile.txt


Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!

To open the file, use the built-in open() function.


The open() function returns a file object, which has a read() method for reading the content of the file:


Example


f = open("demofile.txt", "r")
print(f.read()) 

Read Only Parts of the File


By default the read() method returns the whole text, but you can also specify how many characters you want to return:


Example


Return the 5 first characters of the file:


f = open("demofile.txt", "r")
print(f.read(5))

Read Lines


You can return one line by using the readline() method:


Example


Read one line of the file:


f = open("demofile.txt", "r")
print(f.readline())

By calling readline() two times, you can read the two first lines:


Example


Read two lines of the file:


f = open("demofile.txt", "r")
print(f.readline())
print(f.readline())

By looping through the lines of the file, you can read the whole file, line by line:


Example


Loop through the file line by line:


f = open("demofile.txt", "r")
for x in f:
  print(x)

Close Files


It is a good practice to always close the file when you are done with it.


Example


Close the file when you are finish with it:


f = open("demofile.txt", "r")
print(f.readline())
f.close()

Write to an Existing File


To write to an existing file, you must add a parameter to the open() function:


"a" - Append - will append to the end of the file


"w" - Write - will overwrite any existing content


Example


Open the file "demofile2.txt" and append content to the file:


f = open("demofile2.txt", "a")
f.write("Now the file has more content!")
f.close()

#open and read the file after the appending:
f = open("demofile2.txt", "r")
print(f.read()) 

Example


Open the file "demofile3.txt" and overwrite the content:


f = open("demofile3.txt", "w")
f.write("Woops! I have deleted the content!")
f.close()

#open and read the file after the appending:
f = open("demofile3.txt", "r")
print(f.read())  

Create a New File


To create a new file in Python, use the open() method, with one of the following parameters:


"x" - Create - will create a file, returns an error if the file exist


"a" - Append - will create a file if the specified file does not exist


"w" - Write - will create a file if the specified file does not exist


Example


Create a file called "myfile.txt":


f = open("myfile.txt", "x") 

Result: a new empty file is created!


Example


Create a new file if it does not exist:


f = open("myfile.txt", "w")  

Delete a File


To delete a file, you must import the OS module, and run its os.remove() function:


Example


Remove the file "demofile.txt":


import os
os.remove("demofile.txt")

Check if File exist:


To avoid getting an error, you might want to check if the file exists before you try to delete it:


Example


Check if file exists, then delete it:


import os
if os.path.exists("demofile.txt"):
  os.remove("demofile.txt")
else:
  print("The file does not exist")

Delete Folder


To delete an entire folder, use the os.rmdir() method:


Example


Remove the folder "myfolder":


import os
os.rmdir("myfolder")




Hi I am Pluto.