FILE HANDLING in python to understand basic operations.

FILE HANDLING
 INTRODUCTION
 DATA FILES
 OPENINGANDCLOSING FILES
 READINGANDWRITING FILES
 STANDARD INPUT,OUTPUTAND ERRORSTREAMS

Introduction
 FILE HANDLING is a mechanism by which we
can read data of disk files in python program or
write back data from python program to disk
files.
 So far in our python program the standard input
in coming from keyboard an output is going to
monitor i.e. no where data is stored permanent
and entered data is present as long as program is
running BUT file handling allows us to store data
entered through python program permanently in
disk file and later on we can read back the data

DATA FILES
 It contains data pertaining to a specific
application, for later use. The data files can be
stored in two ways –
 Text File
 Binary File

Text File
 Text file stores information in ASCII OR
UNICODE character. In text file everything will
be stored as a character for example if data is
“computer” then it will take 8 bytes and if the
data is floating value like 11237.9876 it will take
10 bytes.
 In text file each like is terminated by special
character called EOL. In text file some
translation takes place when this EOL character
is read or written. In python EOL is ‘n’ or ‘r’ or
combination of both

Binary files
 It stores the information in the same format
as in the memory i.e. data is stored according
to its data type so no translation occurs.
 In binary file there is no delimiter for a new
line
 Binary files are faster and easier for a
program to read and write than text files.
 Data in binary files cannot be directly read, it
can be read only through python program for
the same.

Steps in Data File Handling
1. OPENING FILE
 We should first open the file for read or write by
specifying the name of file and mode.
2. PERFORMING READ/WRITE
 Once the file is opened now we can either read or
write for which file is opened using various functions
available
3. CLOSING FILE
 After performing operation we must close the file
and release the file for other application to use it,

Opening File
 File can be opened for either – read, write,
append.
SYNTAX:
file_object = open(filename)
Or
file_object = open(filename,mode)
** default mode is “read”

Opening File
myfile = open(“story.txt”)
here disk file “story.txt” is loaded in
memory and its reference is linked to “myfile”
object, now python program will access
“story.txt” through “myfile” object.
here “story.txt” is present in the same
folder where .py file is stored otherwise if disk
file to work is in another folder we have to give
full path.

Opening File
myfile = open(“article.txt”,”r”)
here “r” is for read (although it is by default, other
options are “w” for write, “a” for append)
myfile = open(“d:mydatapoem.txt”,”r”)
here we are accessing “poem.txt” file stored in
separate location i.e. d:mydata folder.
at the time of giving path of file we must use double
backslash() in place of single backslash because in python
single slash is used for escape character and it may cause
problem like if the folder name is “nitin” and we provide path
as d:nitinpoem.txt then in nitin “n” will become escape
character for new line, SO ALWAYS USE DOUBLE
BACKSLASH IN PATH

Opening File
myfile = open(“d:mydatapoem.txt”,”r”)
another solution of double backslash is
using “r” before the path making the string as
raw string i.e. no special meaning attached to
any character as:
myfile = open(r“d:mydatapoem.txt”,”r”)

File Handle
myfile = open(r“d:mydatapoem.txt”,”r”)
In the above example “myfile” is the file object
or file handle or file pointer holding the
reference of disk file. In python we will access
and manipulate the disk file through this file
handle only.

File Access Mode
Text
File
Mode
Binary File
Mode
Description Notes
‘r’ ‘rb’ Read only File must exists, otherwise Python raises
I/O errors
‘w’ ‘wb’ Write only If file not exists, file is created
If file exists, python will truncate
existing data and overwrite the file.
‘a’ ‘ab’ Append File is in write mode only, new data will
be added to the end of existing data i.e.
no overwriting. If file not exists it is
created
‘r+’ ‘r+b’ or ‘rb+’ Read and write File must exists otherwise error is raised
Both reading and writing can take place
w+ ‘w+b’ or ‘wb+’ Write and read File is created if not exists, if exists data
will be truncated, both read and write
allowed
‘a+’
VINOD K
SAC
‘a+b’ or ‘ab+’
UMARVERMA,PGT(CS),
HIN BHARDWAJ, PGT(CS)
Write and read
KV OEF KANPUR&
, KV NO.1TEZPUR
Same as above but previous content will
be retained and both read and write.

Closing file
 As reference of disk file is stored in file handle
so to close we must call the close() function
through the file handle and release the file.
myfile.close()
Note: open function is built-in function used
standalone while close() must be called through file
handle

Reading from File
 To read from file python provide many functions
like :
 Filehandle.read([n]) : reads and return n bytes,
if n is not specified it reads entire file.
 Filehandle.readline([n]) : reads a line of input.
If n is specified reads at most n bytes. Read bytes
in the form of string ending with line character or
blank string if no more bytes are left for reading.
 Filehandle.readlines(): reads all lines and
returns them in a list

Example-3: readline()
SAMPLE FILE

Writing onto files
 After read operation, let us take an example
of how to write data in disk files. Python
provides functions:
 write ()
 writelines()
 The above functions are called by the file
handle to write desired content.
Name Syntax Description
write() Filehandle.write(str1) Writes string str1 to file referenced
by filehandle
Writelines() Filehandle.writelines(L) Writes all string in List L as lines to
file referenced by filehandle.

Example-1: write() using “w” mode

Lets run the
same program
again

Now we can observe that while writing data to file using “w” mode the previous
content of existing file will be overwritten and new content will be saved.
If we want to add new data without overwriting the previous content then we
should write using “a” mode i.e. append mode.

Example-2: write() using “a” mode
New content is
added after previous
content

Example-4: Writing String as a record
to file

Example-5: To copy the content of one
file to another file

FILE HANDLING in python to understand basic operations.

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