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In this Chapter

Introduction to Files

Types of Files

Opening and Closing a

Text File

Writing to a Text File

Reading from a Text File

Setting Offsets in a File

Creating and Traversing a Text File

The Pickle Module

C h a pt e r

2.1 IntroduCtion to FileS

We have so far created programs in Python that

accept the input, manipulate it and display the output. But that output is available only during execution of the program and input is to be entered through the keyboard. This is because the variables used in a program have a lifetime that lasts till the time the program is under execution.

What if we want to store the data that were input

as well as the generated output permanently so that we can reuse it later? Usually, organisations would want to permanently store information about employees, inventory, sales, etc. to avoid repetitive tasks of entering the same data. Hence, data are stored permanently on secondary storage devices for reusability. We store Python programs written in script mode with a .py extension. Each program is stored on the secondary device as a 2

File Handling in

python

There are many ways of trying to understand

programs. People often rely too much on one way, which is called "debugging" and consists of running a partly- understood program to see if it does what you expected. Another way, which ML advocates, is to install some means of understanding in the very programs themselves. - Robi n Milner

Chapter 2.indd 1918-Jun-21 2:29:01 pm

COMPUTER SCienCe - ClaSS XiiFile Handling in pytHon 20 secondary storage media where data are permanently stored for later access.

2.2. typeS oF FileS

a series of bytes stored one after the other. There are which can be opened by any text editor. On the other to access its contents. consisting of alphabets, numbers and other special symbols. Files with extensions like .txt, .py, .csv, etc. using a text editor (e.g., Notepad), we see several lines a way internally. Rather, they are stored in sequence any other encoding scheme, the value of each character and shows us the equivalent character that is readable (\n). However, other characters can be used to indicate by whitespace, but comma (,) and tab (\t) are also

Activity 2.1

notepad and write your name and save it. using Microsoft Word and write your name and save it as well.

Check and compare

in bytes whereas that of .docx is in KBs.

RQO\WKH$6&,,

equivalent of the contents of the many additional information like the author's name, page settings, font of creation and chapter 2.indd 2018-Jun-21 2:29:02 pm COMPUTER SCienCe - ClaSS XiiFile Handling in pytHon The establishes a link between the program and the in the permanent storage. actual content such as image, audio, video, compressed are not human readable. Thus, trying to open a binary and make it unreadable to the supporting application. readable. We can read and write both text and binary

2.3 opening and CloSing a teXt File

with data coming from different sources like databases, so on. Python has the io module that contains different syntax of open() is as follows: which is stored in the variable . We can name we specify in the statement.

The has certain attributes that tells us

false otherwise.

Chapter 2.indd 2118-Jun-21 2:29:02 pm

COMPUTER SCienCe - ClaSS XiiFile Handling in pytHon 22
returns the access mode in which the The directory, then we need to specify the complete path of

The is an optional argument that

to be opened like for reading, for writing, <+> for both reading and writing, for appending at the in text mode that means strings can be read or written. mode that means read/write are performed in terms of )LOH2SHQ0RGHV )LOH0RGH'HVFULSWLRQ)LOH2IIVHWSRVLWLRQ or <+r> or <+wb> or <+a>

Activity 2.2

Some of the other

, , , , . Find out for what purpose each of these are used. offset positions in each case.

Consider the following example.

Chapter 2.indd 2218-Jun-21 2:29:02 pm

COMPUTER SCienCe - ClaSS XiiFile Handling in pytHon 23
is opened myObject. Once we are done with the read/write operations on a a system frees the memory allocated to it. The syntax of is:

Python makes sure that any unwritten or unsaved

The syntax of with clause is:

that is opened using this clause is closed automatically, it provides a simpler syntax.

FRQWHQW P\2EMHFWUHDG

using close() statement. Python will automatically close

2.4 Writing to a teXt File

NoteS chapter 2.indd 2318-Jun-21 2:29:02 pm COMPUTER SCienCe - ClaSS XiiFile Handling in pytHon 24
hand, in append mode, new data will be added at the

ZULWHIRUZULWLQJDVLQJOHVWULQJ

ZULWHOLQHVIRUZULWLQJDVHTXHQFHRIVWULQJV

2.4.1 The write() method

41
note: 2 The

2.4.2 The writelines() method

write() and append() methods? in buffer to the

Chapter 2.indd 2411/9/2021 5:04:45 pm

COMPUTER SCienCe - ClaSS XiiFile Handling in pytHon , the method does not return the code explains the use of &RQWHQWVRIP\quotesdbs_dbs6.pdfusesText_12

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