Python File

• File handling is the most important part of any Web Applications.
• This has several functions for creating, reading, updating, deleting files etc.,

File Handling:

          The key for working with files in Python is the open() function.

Syntax: open(filename, mode)

There are four different methods for opening a file:

"r" - Read - Default value. Opens a file for reading, error if the file does not exist.

"a" - Append - Opens a file for appending, creates the file if it does not exist.

"w" - Write - Opens a file for writing, creates the file if it does not exist.

"x" - Create - Creates the specified file, returns an error if the file exists.

In addition you can specify if the file should be handled as binary or text mode:

"t" - Text - Default value. Text mode.

"b" - Binary - Binary mode(e.g., images)

Note: Make sure the file exists, or else you will get an error.

Syntax:

f = open("demofile.txt", "rt")

Because "r" for read, and "t" for text are the default values, you do not need to specify them.

Python File Open:

Open a file on the server:

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

E.g.,

f = open("demo.txt", "r")

print(f.read( ))

Read Only the Parts of the File:

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

E.g.,

f = open("demofile.txt", "r")

print(f.read(5))

Read Lines:

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

E.g.,

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

print(f.readline( ))

If you want to first two lines, this can be done by calling readline( ) two times.

By looping  through the lines of the file, we can read the entire file line by line.,

E.g.,

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

for x in f:

    print(x)

Closing a File:

          It is always good to close a file when we have done using the file handling process by using the close( ) method.

NOTE: You should always close the file, in few cases, due to buffering, changes made to a file may not show until you close the file respectively.