ClassXII - Computer Science

 

    Data File Handling

    To store the data in secondary storage device through Python program, Data File Handling mechanism is used. To handle several types of data, different types of files are used. 

 
 Video: (5:45 min) Need of Data File Handling and reading a simple text file using Python

Types of files:

1. Text File
2. Binary File
3. CSV file

Text file: A text file can be understood as a sequence of characters consisting of alphabets, numbers and other special symbols. Files with extensions like .txt, .py, .csv, etc. are some examples of text files.

Binary file: Binary file represent the actual content such as image, audio, video, compressed versions of other files, executable files, etc. These files are not human readable. Binary files are stored in a computer in a sequence of bytes.

CSV (Comma Separated Value) file: These files are text file only except its extension is .csv. They can be opened in spreadsheet format.

File open Mode:

File mode             Description
'r'                           Open text file for reading. Raises an I/O error if the file does not exist.

'w'                          Open the file for writing. Truncates the file if it already exists. Creates a new file if it does not exist.
'a'                           Open the file for writing. The data being written will be inserted at the end of the file. Creates a new file if it does not exist.
'r+' or '+r'              Open the file for reading and writing. Raises an I/O error if the file does not exist.
'a+' or '+a'             Open the file for reading and writing. The data being written will be inserted at the end of the file. Creates a new file if it does not exist.
'rb'                        Open the file for reading in binary format. Raises an I/O error if the file does not exist.

'ab'                        Open the file for appending in binary format. Inserts data at the end of the file. Creates a new file if it does not exist.
'wb+' or '+wb'       Open the file for reading and writing in binary format. Truncates the file if it already exists. Creates a new file if it does not exist.

 Video: (7:46 min)  File Modes and Types of File

read(): Function: This function reads the byte(s) of stream or entire text from current position of file pointer from text file and returns it in the form of string.

#Program to demonstrate read function
f=open('a.txt','r')
x=f.read(10)
print(x)
input()
x=f.read(5)
print(x)
input()
x=f.read(5)
print(x)
input()
x=f.read()
print(x)
input()
f.close()

readline(): Function: This function reads a single line from current position of file pointer from text file and returns it in the form of string. The function stops reading as soon as it encounters '\n' (newline) character.

#Program to demonstrate readline function
f=open('a.txt','r')
x=f.readline()
print(x)
input()

x=f.readline(5)
print(x)
input()

x=f.readline(2)
print(x)
input()

x=f.readline()
print(x)
input()

# ...... More number of readline functions can be used depending upon the content of text.

f.close()

readlines() function: This function reads all the lines of text file and stores them in the form of list.

#Program to demonstrate readlines function

f=open('a.txt','r')
x=f.readlines()
print(x)
input()

f.close()

Video: (19:40 min) Text Files (read(), readline() and readlines()

write() and writelines() functions: This function writes the text from python program to text file. 

f=open("abc.txt","a")

f.write("1111\n")

f.writelines['123\n','xyz\n','4563\n'])

f.close()

 Video: (11:02 min) Text Files - write() and writelines()

Reading and writing Binary files:

# Writing in binary file

import pickle

f=open('a.dat','wb')

L=[34,56,3,12,87,7]

pickle.dump(L,f)

f.close()

# Reading from binary file

import pickle

f=open('a.dat','rb')

x=pickle.load(f)

print(x)

f.close()

  Video: (09:44 min) Binary Files - load() and dump()