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Part9-File-Handling.md

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File handling with Python

File:

  • File is a named location on a secondary storage device where data are permanently stored for later access.

File Handling:

  • The process of creating a file, storing the data in it, retrieving data from it and appending further information is said to be File Handling.

Does python support file handling:

  • Python supports file handling like many other programming languages.
  • There are many programming languages that supports file handling, in some languages this topic is a bit complicated, but in python file handling is very easy.

Use of file handling in Python:

  • File handling provies various modes(read mode, write mode etc) to operate a file.
  • We can create a new file using python code, open existing files, write in files ,read data from files and many more such options.

There are mainly two types of data files

  • Text file
  • Binary file

Text file

  • A text file can be understood as a sequence of characters consisting of alphabets, numbers and other special symbols
  • File extensions like .txt, .py, .csv, etc. are few examples of text files.
  • Each line of a text file is stored as a sequence of ASCII equivalent of the characters.
  • This is terminated by a special character called the End of Line (EOL).

Binary file

  • Binary file consists of data stored as a stream of bytes.
  • Binary files are mainly used to store data beyond text such as images, executables, etc.

Opening and Closing Files

Python consists of various built in functions and methods to manipulate files. These functions and methods bascically work on a file object

  • The Open() Function:

    • Python built in open() function is used to open the file for reading or writing to it.
    • The syntax of open() is:
    Syntax
    fileObj= open(file_name[,access_mode])
    • Here,
      • file_name is string value that specifies name of the file that you want to access.
      • access_mode indicates the mode in which the file is supposed to be opened i.e., read,write, etc.

  • The Close() Function:

    • The close() method is used to close the file object.
    • Once a file object is closed, you cannot further read from or write into the file that is associated with this file object.
    • The Syntax of close() is:
      |Syntax:| |-| |fileobj.close()|

Access Modes in Python

Modes Purpose
r Opens the file in read-only mode
rb Opens the file in read-only binary format mode
r+ Opens the file in both read and write mode
rb+ Opens the file in both read and write mode in binary format
w Opens the file in write mode. If the file doesn't exists then a new file will be created.
wb Opens the file in write mode for binary format only
w+ Opens the file in both read and write mode. If the file doesn't exist, a new file is created for reading as well as writing.If the file already exists then contents are overwritten
wb+ Opens the file in both read and write for binary format only.If the file doesn't exist, a new file is created for reading as well as writing.If the file already exists then contents are overwritten
a Opens a file for appending.The pointer is placed at the end of the file if the file exists. If file doesn't exist, it creates a new file for writing.
ab Opens a file in binary format for appending.The pointer is placed at the end of the file if the file exists. If file doesn't exist, it creates a new file for writing.
a+ Opens a file for both reading and appending.The pointer is placed at the end of the file if the file exists. If file doesn't exist, it creates a new file for reading and writing.
ab+ Opens a file in binary for both reading and appending.The pointer is placed at the end of the file if the file exists. If file doesn't exist, it creates a new file for reading and writing.

If no mode is specified then 'r' is considered as default mode.

The File Object Attributes

Attribute Information Obtained
file.mode it returns the access mode in which file is opened
file.name it returns the name of the file
file.close it is used to close the file
file.closed it returns True if file is closed,False if not.
read([size]) It reads the specified number of bytes(the size specified) from the file.
readline([size]) It is used to read one entire line from a file
tell() This returns the current position of file pointer.
write(str) This writes a string into the file.
writelines(sequence) This writes a sequence of strings into the file

Examples

file = open("devincept.txt", "r") 
print (file.read())
DevIncept 
Learn by Developing!

file = open('a.txt','w')
file.write("I want do an Internship ")
file.close()
file = open('a.txt','a')
file.write("\nI Love DevIncept")
file.close()
file=open("a.txt",'r')
print(file.read())
This is words motivates me
I Love DevIncept

f = open('story.txt', 'r') 
text = f.read(53)  
print(text) 
f.close() 
Once upon a time, in a field not too far from you, th

f = open('story.txt','r')
text = f.readline(20) 
print(text) 
f.close() 
Once upon a time, in

f = open('story.txt', 'r') 
text = f.readlines(25) 
print(text) 
f.close() 
['Once upon a time, in a field not too far from you, there was an energetic and happy hare and a sleepy tortoise.\n']

f = open('B.txt','w+') 
lines = "It's a new day\n"
f.write(lines) 
f.close() 
f = open('C.txt', 'a+') 
lines = "New day!"
f.write(lines) 
f.close() 
file=open("devincept.txt","wb")
print("Name of the file:",file.name)
print("File is closed",file.closed)
print("File has been opened in",file.mode,"mode")
Name of the file: devincept.txt
File is closed False
File has been opened in wb mode

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