File handling is an important part of any web
application.
Python has several functions for creating, reading,
updating, and deleting files.
The
key function for working with files in Python is the open() function.
The open() function takes two
parameters; filename, and mode.
There are four different methods (modes) for
opening a file:
"r" - Read - Default value. Opens a
file for reading, error if the file dont 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)
Syntax
To open a file for reading it is enough to specify
the name of the file:
f = open("demofile.txt")
The code above is the same as:
f = open("demofile.txt", "rt")
Because "r" for read,
and "t" for text are the default values,
you do not need to specify them.
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())
C:\Users\My
Name>python demo_file_open.py
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Read Files
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))
C:\Users\My
Name>python demo_file_open2.py
Hello
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())
C:\Users\My
Name>python demo_file_readline.py
Hello! Welcome to demofile.txt
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())
C:\Users\My Name>python demo_file_readline2.py
Hello! Welcome to demofile.txt
This file is for testing purposes.
Read the Whole File:
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)
C:\Users\My Name>python demo_file_readline3.py
Hello! Welcome to demofile.txt
This file is for testing purposes.
Good Luck!
Comments
Post a Comment