The random access memory is volatile and all its contents are lost once a program terminates.
In order to persist the data forever, we use files.
A file is data stored in a storage device. A python program can talk to the file by reading content from it and writing content to it.
Types of Files
There are 2 types of files:
- Text files (.txt, .c, etc)
- Binary files (.jpg, .dat, etc)
Python has a lot of functions for reading, updating, and deleting files.
Opening a file
Python has an open() function for opening files. It takes 2 parameters: filename and mode.
open(“this.txt”, “r”)
Here, “this” is the file name and “r” is the mode of opening (read mode)
Reading a file in Python
f = open(“this.txt”, “r”) #Opens the file in r mode
text = f.read() #Read its content
print(text) #Print its contents
f.close() #Close the fie
We can also specify the number of characters in read () function:
f.read(2) #Reads first 2 characters
Other methods to read the file
We can also use f.readline() function to read on full line at a time.
f.readline() #Reads one line from the file
Modes of opening a file
r – open for reading
w – open for writing
a – open for appending
+ -> open for updating
‘rb’ will open for read in binary mode
‘rt’ will open for read in text mode
Writing Files in Python
In order to write to a file, we first open it in write or append mode after which, we use the python’s f.write() method to write to the file!
f = open(“this.txt”, “w”)
f.write(“This is nice”) #Can be called multiple times
f.close()
With statement
The best way to open and close the file automatically is the “with” statement.
with open(“this.txt”) as f:
f.read()
#There is no need to write f.close() as it is done automatically
Chapter 9 – Practice Set
- Write a program to read the text from a given file “poems.txt” and find out whether it contains the word ‘twinkle’.
- The game() function in a program lets a user play a game and returns the score as an integer. You need to read a file “Hiscore.txt” which is either blank or contains the previous Hi-score. You need to write a program to update the Hi-score whenever game() breaks the Hi-Score.
- Write a program to generate multiplication tables from 2 to 20 and write it to the different files. Place these files in a folder for a 13- year old boy.
- A file contains the word “Donkey” multiple times. You need to write a program which replaces this word with ###### by updating the same file.
- Repeat program 4 for a list of such words to be censored.
- Write a program to mine a log file and find out whether it contains ‘python’.
- Write a program to find out the line number where python is present from question 6.
- Write a program to make a copy of a text file “this.txt”.
- Write a program to find out whether a file is identical and matches the content of another file.
- Write a program to wipe out the contents of a file using python.
- Write a python program to rename a file to “renamed_by_python.txt”.
beginner's 