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

Objectives

1. Use the for loop.
2. Use range() function.

System Specifications

• Ubuntu Linux 14.04 operating system
• Python 3.4.3
• IPython 5.1.0

Pre-requisite

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

If not, see the relevant Python tutorials on this website.

Syntax: For

for <loop variable> in sequence:

   <statement 1>

   <statement 2> 

   ...
   <statement n>

Highlight according to narration

for statement iterates over the members of a sequence in order, executing the block each time.

Here the loop variable takes the value of the item inside the sequence on each iteration.

For each item, the loop body is executed.

ipython3

Now, type ipython3 and press Enter.

%pylab and press Enter.

Type %pylab and press Enter.

for num in numbers:

   print(“sqrt of”, num, “is”, num**0.5)

print("This is outside for-loop")

The numbers are: 4, 9, 16, 25, and 36.

Note that here we used two variables,

• numbers - which is a list of numbers
• num - which is the element of list under consideration, in each cycle of the for loop.

The variable names can be any of your choice.

Every statement in loop starts with 4 spaces.

In this example, it is only a single statement in the block.

print("This is outside for-loop")

It means that it is not a part of the for loop.

And the lines after that don't fall in the scope of the for loop.

This marks the importance of white-spaces in Python.

Let us clear the terminal.

Save & run script

Highlight the output

%run -i sqrt_num_list.py

sqrt of 4 is 2.0

sqrt of 9 is 3.0

sqrt of 16 is 4.0

sqrt of 25 is 5.0

sqrt of 36 is 6.0

This is outside for-loop

percent run minus i filename and press Enter.

%run -i sqrt_num_list.py

sqrt of 4 is 2.0

sqrt of 9 is 3.0

sqrt of 16 is 4.0

sqrt of 25 is 5.0

sqrt of 36 is 6.0

This is outside for-loop

This is the print statement output executed after the for loop.

Exercise 1

• Use the same example we used in sqrt_num_list.py

• Type each line of the code in the IPython interpreter prompt.

• Skip the line: print("This is outside for-loop")

Type

numbers = [4, 9, 16, 25, 36]

for num in numbers:

Press Enter

Type,

numbers equal to inside square brackets 4, 9, 16, 25, 36 and press Enter

for num in numbers colon Press Enter

And the cursor is not after the three dots but, there are four spaces from the three dots.

Highlight the three dots

The three dots tell you that you are inside a block.

'print(“sqrt of”, num, '“is”, num**0.5)

print inside parentheses inside quotes sqrt of comma num comma inside quotes is comma num asterick asterick which is raised to power of 0.5 and press Enter

But still the interpreter is showing three dots.

This means that you are still inside the block.

press Enter twice

Highlight the output

%run -i sqrt_num_list.py

sqrt of 4 is 2.0

sqrt of 9 is 3.0

sqrt of 16 is 4.0

sqrt of 25 is 5.0

sqrt of 36 is 6.0

This is outside for-loop

range() function

The syntax is: range start comma stop comma step

range() function

For example:

range inside parentheses one comma twenty comma two – generates integers from 1 to 19 with step of 2

range inside parentheses twenty – generates integers from 0 to 19

Highlight output

Exercise 2

Execute this in the Python interpreter.

Open a new terminal by pressing Ctrl+Alt+T keys simultaneously.

Type

python

for i in range(1, 11):

press Enter

Start the Python interpreter by issuing the command python in the new terminal and press Enter.

Type,

for i in range inside parentheses one comma eleven colon and press Enter

Highlight the cursor

So we have to indent the block.

Type

print(i, "cube is", i**3)

So enter four spaces and then type the following.

print inside parentheses i comma inside quotes cube is comma i raised to power of three press Enter.

press Enter

To get out of the block, press Enter once again.

• how to use the Python interpreter and

• the IPython interpreter to specify blocks.

Exercise 3

The problem can be solved by just using the range() function.

for i in range(1, 50, 2):

   print(i)

press Enter twice

Let us clear the terminal.

for i in range inside parentheses one comma fifty comma two colon

press Enter

print inside parentheses i press Enter twice.

Highlight 1 and 50 in range function

The second parameter is the end of the range.

The third parameter is for stepping through the sequence.

Here we gave two which means we are skipping every alternate element.

Summary

In this tutorial, we learnt to,

1. Create blocks in python using for
2. Indent the blocks of code
3. Iterate over a list using for loop
4. Use the range() function

Assignment

1. Indentation is not mandatory in Python

• True
• False

2. Write a for loop to print the product of all natural numbers from 1 to 20.

3. What will be the output of:

range(1, 5)

Solution of self assessment questions on slide

1. False, Indentation is essential in python.

2. y equal to one

for x in range inside parentheses one comma twenty one colon

y into equal to x

print inside parentheses y

3. range(1, 5) will produce a list of integers from 1 to 4 i.e. [1,2,3,4]

Forum

Fossee Forum

Textbook Companion

Acknowledgment

http://spoken-tutorial.org

For more details, visit this website.

Thank you.