Difference between revisions of "Python-3.4.3/C2/Getting-started-with-files/English"

Objectives

1. Open a file.
2. Read the contents of the file line by line.
3. Read the entire content of the file at once.
4. Append the lines of a file to a list.
5. Close the file.

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3
• IPython 5.1.0

Pre-requisite

• Lists and
• for statement

If not, see the pre-requisite Python tutorials on http://spoken-tutorial.org

Open a file

Highlight according to narration: (open and fileobject)

syntax:

file_object = open(“filename”, “mode”)

Filename - name of the file to be opened.

Mode- indicates how the file is going to be opened.

Open() function returns a file object.

The syntax is shown here:

Filename - is the name of the file to be opened.

Mode- This indicates how the file is going to be opened.

Open a file

syntax:

f = open(“filename”, “mode”)

r- Read mode

w- Write mode

a -Appending mode

r+ - Read and Write

w- is for Write mode

a - represents Appending mode and

r+ - for both Read and Write mode

Specifying mode is optional.

We will be using this text file for our demonstration.

Please download it in Home directory and use it.

ipython3

Now, type ipython3 and press Enter.

%pylab and press Enter.

Type %pylab and press Enter.

f = open('pendulum.txt')

f is equal to open inside parentheses inside quotes pendulum dot txt

Here the mode is not specified. By default, it is ‘r’.

f

The file object f, shows the filepath and mode of the file, which is open.

Highlight filepath and mode 'r'

As you can see, this file is open in read only mode.

pend = f.read()

Highlight pend= f.read()

pend equal to f dot read open and close parentheses.

We use the read method to read all the contents of the file into the variable, pend

Press Enter

To use read method we use the file object dot read method.

print(pend)

print inside parentheses pend.

Press Enter

pendHighlight output

We can see the newline characters as well in the output.

We use the method splitlines to split a file of data into list of lines.

Type

pend_list = pend.splitlines()

pend_list

Highlight the output

Type

pend_list equal to pend dot splitlines open and close parentheses

Press Enter

Type

pend underscore list

Press Enter

We got the data into list of lines.

This is because the string pend is split on the newline characters.

f.close()

Let us close the file opened into f.

Type f dot close open and close parentheses

Highlight closed file

Exercise 1

Re-open the file pendulum.txt with f as the file object.

Recall, that we have closed the file earlier.

f = open('pendulum.txt')

f is equal to open inside parentheses inside quotes pendulum.txt

for line in f:

print(line)

Let us iterate over the file line-wise and print each of the lines.

Type

for line in f colon press Enter

four spaces print inside parentheses line

Highlight line

We could have used any other variable name, but line seems meaningful enough.

Highlight line

line_list = []

Type,

line underscore list equal to open and close square brackets.

Highlight according to narration.

for line in open('pendulum.txt'):

line_list.append(line)

for line in open inside parentheses inside quotes pendulum dot txt colon press enter

four space line underscore list dot append inside parentheses line

Here, the for loop reads the file pendulum.txt line-by-line .

The append method will add each of the line to the list, line_list.

This will save us the trouble of closing the file, each time we open it.

Type line_list and press Enter

Highlight output

Type line_list and press Enter.

Highlight newline character

This will be covered in the further tutorial on strings.

Summary

1. Open and close files using the open and close methods respectively.
2. Read the data in the files as a whole, by using the read method.

Summary

1. Append the lines of a file to a list using the append method within the for loop.

Assignment

1. The open function returns a

• string
• list
• file object
• function

2. What does the function splitlines() do.

• Displays the data as strings, all in a line
• Displays the data line by line as strings
• Displays the data line by line but not as strings

Solutions

1. open function returns a file object
2. splitlines() displays the data line by line as strings

Forum

Fossee Forum

Textbook Companion

Acknowledgment

http://spoken-tutorial.org

For more details, visit this website.

Thank you.