File Handling concept in python

 File Handling:-

• Programming Languages are good at processing the data, But they cannot store the data permanently. 

• Because programming Languages programs memory will be allocated in RAM.

• RAM is a volatile so that once the program execution is over the memory which is allocated for that program is going to be de-allocated.

• If we don't store the data permanently we cannot able to store the data in future.

• In order to store the data permanently we use Files, RDBMS or ORDBMS(Object relational database management system), NOSQL.

• File is a named location on the disk to store related information.It is used to permanently store data in a non-volatile memory (e.g. hard disk). Since, random access memory (RAM) is volatile which loses its data when computer is turned off, we use files for future use of the data.

• Python Language is providing API or Libraries to perform the operations on the files.

• Before going to perform the read/write operations on the files first we have to open the files. We can open the files by calling the open function of builtins module.

• At the time of opening the file we need to specify the mode of the file

MODE	DESCRIPTION
r	Opens the file for reading (default)
w	Opens the file in writing. Creates a new file if it does not exist or truncate the file if it exists.
x	Opens the file in exclusive creation. If the file already exists, the operation fails.
a	Open for appending at the end of the file. Creates a new file of it does not exists.
t	Opens in text mode(Default)
b	Opens in binary mode.
+	Opens file for updating(Reading and Writing)

• After executing the open function it returns file object.

• File Object provides some methods to read or write the data to the files. 

• After performing the operations on the file we have to close the file. 

• We can close the file by calling close( ) method on the file Object.

in Python, a file operation takes place in the following order.

1.     Open a file

2.     Read or write (perform operation)

3.     Close the file

Opening a File:

Python has a built-in function open( ) to open a file. This function returns a file object, also called a handle, as it is used to read or modify the file accordingly.

f = open("test.txt")    # open file in current                                                      directory

f = open("C:/Python33/README.txt")  

                                 # specifying full path

f = open("test.txt")      # equivalent to 'r' or 'rt'

f = open("test.txt",'w')  # write in text mode

f = open("img.bmp",'r+b') # read and write in                                             binary mode

Closing a File:

• When we are done with operations to the file, we need to properly close it. Python has a garbage collector to clean up un-referenced objects. But we must not rely on it to close the file. Closing a file will free up the resources that were tied with the file and is done using the close( ) method.

f = open("test.txt")

f.close()

Reading data from the file:

x=open("test.txt")

print(x.read( ))

x.close( )

Writing data to file:

x=open("z.txt","w")

x.write("Welcome")

x.close( )

Appending data to file:

x=open("z.txt","a")

x.write("Python")

x.close( )

Python File Methods
Method	Description
close()	Close an open file. It has no effect if the file is already closed.
detach()	Separate the underlying binary buffer from the TextIOBaseand return it.
fileno()	Return an integer number (file descriptor) of the file.
flush()	Flush the write buffer of the file stream.
isatty()	Return True if the file stream is interactive.
read(n)	Read at most n characters form the file. Reads till end of file if it is negative or None.
readable()	Returns True if the file stream can be read from.
readline(n=-1)	Read and return one line from the file. Reads in at most nbytes if specified.
readlines(n=-1)	Read and return a list of lines from the file. Reads in at most n bytes/characters if specified.
seek(offset,from=SEEK_SET)	Change the file position to offset bytes, in reference tofrom (start, current, end).
seekable()	Returns True if the file stream supports random access.
tell()	Returns the current file location.
truncate(size=None)	Resize the file stream to size bytes. If size is not specified, resize to current location.
writable()	Returns True if the file stream can be written to.
write(s)	Write string s to the file and return the number of characters written.
writelines(lines)	Write a list of lines to the file.

Working with file methods:

x=open("z.txt")

print(x.tell( ))

print(x.read(3))

print(x.tell( ))

print(x.read(4))

print(x.tell( ))

x.seek(5)

print(x.tell( ))

print(x.read(10))

print(x.tell( ))

x.close( )


working  "with" statement:



with open('test.txt') as f1:
    print(f1.read())

    f1.close()