Difference between revisions of "Python-3.4.3/C2/Getting-started-with-for/English"
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− | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[Ipython Terminal]</nowiki>Type | + | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[Ipython Terminal]</nowiki> |
+ | Type | ||
'''<nowiki>numbers = [4, 9, 16, 25, 36]</nowiki>''' | '''<nowiki>numbers = [4, 9, 16, 25, 36]</nowiki>''' | ||
− | '''for num in numbers: '''Press '''Enter''' | + | '''for num in numbers: |
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+ | '''Press '''Enter''' | ||
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Switch to the '''terminal'''. | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Switch to the '''terminal'''. | ||
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The syntax is: '''range start ''comma'' stop ''comma'' step''' | The syntax is: '''range start ''comma'' stop ''comma'' step''' | ||
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+ | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Show Slide | ||
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+ | '''range()''' function | ||
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+ | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| | ||
For example: | For example: | ||
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| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[Terminal]</nowiki> | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[Terminal]</nowiki> | ||
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'''python''' | '''python''' | ||
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| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[Python Terminal]</nowiki> | | style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| <nowiki>[Python Terminal]</nowiki> | ||
+ | Type | ||
'''print(i, "cube is", i**3)''' | '''print(i, "cube is", i**3)''' |
Latest revision as of 19:40, 8 January 2018
Title of script: Getting started with for loops
Author: Trupti, Thirumalesh H S
Keywords:Python, IPython, for loop, blocks, indent, iterate, loop
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Show Slide | Hello Friends. Welcome to the tutorial on "Getting started with for loops". |
Show Slide
Objectives |
At the end of this tutorial, you will be able to,
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System Specifications |
To record this tutorial, I am using,
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Show Slide:
Pre-requisite If not, see the relavant Python tutorials on http://spoken-tutorial.org |
To practice this tutorial, you should know how to use lists.
If not, see the relevant Python tutorials on this website. |
First let us see the syntax of for loop. | |
Show slide
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.
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We will see an example of for loop and how to execute it. | |
[Terminal]
ipython3 |
Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.
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[IPython console]
%pylab and press Enter. |
Let us initialise the pylab package.
Type %pylab and press Enter. |
Open your text editor. | Open your text editor. |
Highlight according to narration | Let us write a for loop. Type the code as shown here: |
numbers = [4, 9, 16, 25, 36]
for num in numbers: print(“sqrt of”, num, “is”, num**0.5) print("This is outside for-loop") |
Here the loop variable iterates over a list of numbers and finds the square root of each number.
The variable names can be any of your choice. |
Highlight the line print(“sqrt of”, num, “is”, num**0.5) | Note that a colon after the for statement indicates the starting of loop body.
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Highlight the line print(“sqrt of”, num, “is”, num**0.5) | It means that, the line is a block of code in for loop.
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Highlight the fifth line -
print("This is outside for-loop") |
Note that the line print("This is outside for-loop") is not indented.
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Highlight indentation | Thus each block is separated by the indentation level.
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Save the file as sqrt_num_list.py | Save the file as sqrt_num_list.py in the home directory. |
switch back to your terminal. Clear the terminal | Now switch back to your terminal.
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[Ipython 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 |
Run the script using the run command as-
percent run minus i filename and press Enter. |
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 |
We get the square root of the given numbers executed by the for loop.
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Show Slide
Exercise 1 |
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[Ipython Terminal]
Type numbers = [4, 9, 16, 25, 36] for num in numbers: Press Enter |
Switch to the terminal.
numbers equal to inside square brackets 4, 9, 16, 25, 36 and press Enter
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Highlight the three dots | You will notice that, the prompt changes to three dots.
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[Ipython Terminal]
Highlight the three dots |
Please note that IPython automatically indents the block.
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[Ipython Terminal] Type
'print(“sqrt of”, num, '“is”, num**0.5) |
Now type the rest of the for loop.
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 |
[Ipython Terminal] | Now we have finished the statements in the block.
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[Ipython Terminal]
press Enter twice |
To exit from the block, press Enter key twice without entering anything else. |
[Ipython Terminal]
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 |
It printed the square root of each number in the list, which was executed in the for loop. |
Next we will see about range built-in function in Python. | |
Show Slide
range() function |
range() function generates a list of integers.
The syntax is: range start comma stop comma step |
Show Slide
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 |
[Ipython Terminal]
Highlight output |
Note that the ending number that you specify will not be included in the list. |
Show Slide
Exercise 2 |
Find out the cube of all the numbers from one to ten.
Execute this in the Python interpreter. |
Open a new terminal. | Let us now try to run the for loop in a Python terminal window.
Open a new terminal by pressing Ctrl+Alt+T keys simultaneously. |
[Terminal]
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 |
[Python Terminal]
Highlight the cursor |
We will see that this time it shows three dots, but the cursor is close to the dots.
So we have to indent the block. |
[Python Terminal]
Type print(i, "cube is", i**3) |
The Python interpreter does not indent the code automatically.
print inside parentheses i comma inside quotes cube is comma i raised to power of three press Enter. |
[Python Terminal]
press Enter |
Now when we hit Enter, we still see the three dots.
To get out of the block, press Enter once again. |
[Python Terminal] | Okay! So the main thing we learnt here is -
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Show Slide
Exercise 3 |
Print all the odd numbers from 1 to 50. |
[IPython Terminal] | Let us do it in our IPython interpreter for ease of use.
The problem can be solved by just using the range() function. |
[IPython Terminal] Type
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
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[IPython Terminal]
Highlight 1 and 50 in range function |
The first parameter is the starting number of the sequence.
The second parameter is the end of the range. |
Highlight third parameter i.e. 2 | Note that the sequence does not include the ending number.
The third parameter is for stepping through the sequence. Here we gave two which means we are skipping every alternate element. |
Show Slide
Summary |
This brings us to the end of the tutorial.
In this tutorial, we learnt to,
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Assignment |
Here are some self assessment questions for you to solve
1. Indentation is not mandatory in Python
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) |
Show Slide
Solution of self assessment questions on slide |
And the answers,
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] |
Show Slide
Forum |
Please post your timed queries in this forum. |
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Fossee Forum |
Please post your general queries on Python in this forum. |
Show Slide
Textbook Companion |
FOSSEE team coordinates the TBC project. |
Show Slide
Acknowledgment |
Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India.
For more details, visit this website. |
Previous slide | This is Trupti Kini from IIT Bombay signing off.
Thank you. |