Python
File Handling
File handling is an important part of any web
application. Generally, we divide files in two
categories, text file and binary file. Text files are simple text whereas the
binary files contain binary data which is only readable by computer.
File Opening
To open a file we use open() function. It
requires two arguments, first the file path or file name, second which mode it
should open.
There are four different methods (modes) 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
As we know file should be handled as binary or text
mode
"t"
- Text - Default value. Text mode
"b"
- Binary - Binary mode (e.g. images)
Example,
We can also neglect “r” and “t” as they are default values.
We can also specify the exact path of the file in as
same.
File
reading
To read the whole file at
once we use, read().
If you call read() again it will return empty
string as it already read the whole file.
readline() can help
you to read one line each time from the file.
To read all the lines in a list we use readlines()
method.
Let us write a program which will take the file name as the input from the user and show the content of the file in the console.
As you see
we used close().
Note: - All
examples above, I haven’t mentioned about closing of a file, but its important
in each and every case.
Always make
sure you explicitly close each open file, once its job is done and you have no
reason to keep it open. Because
·
There is an upper limit to the
number of files a program can open. If you exceed that limit, there is no
reliable way of recovery, so the program could crash.
·
Each open file consumes some
main-memory for the data-structures associated with it, like file
descriptor/handle or file locks etc. So you could essentially end-up wasting
lots of memory if you have more files open that are not useful or usable.
·
Open files always stand a chance of
corruption and data loss.
Note :- Using with statement will look over
the file closing weight.
File writing
Let us open a file then we will write some random text
into it by using the write() method. We can also pass the file object to
the print function call, so that it writes in the file.
