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Diffstat (limited to 'writing_python_scripts/script.rst')
| -rw-r--r-- | writing_python_scripts/script.rst | 241 |
1 files changed, 207 insertions, 34 deletions
diff --git a/writing_python_scripts/script.rst b/writing_python_scripts/script.rst index 0729efd..e537859 100644 --- a/writing_python_scripts/script.rst +++ b/writing_python_scripts/script.rst @@ -20,22 +20,51 @@ Script ------ -{{{ Show the slide containing title }}} +.. L1 -Hello friends and welcome to the tutorial on "Writing Python scripts" +{{{ Show the first slide containing title, name of the production +team along with the logo of MHRD }}} -{{{ Show the slide containing the outline slide }}} +.. R1 -In this tutorial, we shall learn +Hello friends and welcome to the tutorial on "Writing Python scripts". - * How to write Python scripts +.. L2 -Often we will have to reuse the code that we haave written. We do that by -writing functions. Functions are bundled into packages and are imported as and -when required in other scripts. +{{{ Show the slide containing the objectives }}} -Let us first write a function that computes the gcd of two numbers and save it -in a script. +..R2 + +At the end of this tutorial, you will be able to, + + 1. Understand what is importing. + #. Write your own Python modules. + #. Understand the ``__name__=="__main__"`` idiom + +.. L3 + +{{{ Switch to the pre-requisite slide }}} + +.. R3 + +Before beginning this tutorial,we would suggest you to complete the +tutorial on "Using Python modules". + +.. R4 + +Often we will have to reuse the code that we have written. We do that by +writing functions. Functions are bundled into packages and are imported +as and when required in other scripts. + +.. L4 + +.. R5 + +Let us first write a function that computes the gcd of two numbers and +save it in a script.Open an editor and type the code.Please take care +of the indentation. + +.. L5 {{{ Open an editor and start typing out the following code }}} :: @@ -47,11 +76,14 @@ in a script. return a -We shall write a test function in the script that tests the gcd function every -time the script is run. +.. R6 + +We shall write a test function in the script that tests the gcd function +every time the script is run. -{{{ Add to the script }}} +.. L6 +{{{ Add the following lines to the script }}} :: if gcd(40, 12) == 4: @@ -59,26 +91,57 @@ time the script is run. else: print "The GCD function is wrong" +.. L7 + +{{{ Show slide containing GCD code }}} +{{{ Keep open for sometime and then continue }}} + +.. R7 + +.. R8 + Let us save the file as script.py in ``/home/fossee/gcd_script.py`` +.. L8 + +{{{ Save the script as ``gcd_script.py`` }}} + +.. R9 + We shall run the script by typing + +.. L9 + +{{{ Open a terminal }}} :: - $ python /home/fossee/gcd_script.py + python /home/fossee/gcd_script.py + +.. R10 We can see that the script is executed and everything is fine. -What if we want to use the gcd function in some of our other scripts. This -is also possible since every python file can be used as a module. +What if we want to use the gcd function in some of our other scripts. +This is also possible since every python file can be used as a module. But first, we shall understand what happens when you import a module. +.. L10 + +.. R11 + Open IPython and type + +.. L11 + +{{{ Open another terminal and type ipython }}} :: import sys sys.path +.. R12 + This is a list of locations where python searches for a module when it encounters an import statement. @@ -94,40 +157,83 @@ working directory is also searched. Alternatively, we can also import the module if we are working in same directory where the script exists. +.. L12 + +.. L13 + +{{{ Close the current terminal }}} + +.. R13 + +.. R14 + Since we are in /home/fossee, we can simply do + +.. L14 + +{{{ Switch to the first terminal }}} :: - import gcd_script + import gcd_script.py + +.. R15 -We can see that the gcd_script is imported. But the test code that we added at -the end of the file is also executed. +We can see that the gcd_script is imported. But the test code that we +added at the end of the file is also executed. -But we want the test code to be executed only when the file is run as a python -script and not when it is imported. +But we want the test code to be executed only when the file is run as +a python script and not when it is imported. This is possible by using ``__name__`` variable. -First, we shall look at how to use the idiom and then understand how it works. +First, we shall look at how to use the idiom and then understand how +it works. + +.. L15 + +.. L16 + +{{{ Switch to slide, __name__ variable }}} -Go to the file and add +.. R16 + +Go to the file and add this line as the beginning of the code +and indent the code accordingly. + +.. L17 + +{{{ Switch to gcd_script.py and add this line after the + line ``return a`` }}} :: if __name__ == "__main__": - -before the test code and indent the test code. + +.. R17 +.. R18 + Let us first run the code. + +.. L18 + +{{{ Switch back to the terminal }}} :: - $ python gcd_script.py + python gcd_script.py + +.. R19 We can see that the test runs successfully. Now we shall import the file + +.. L19 :: import gcd_script +.. R20 + We see that now the test code is not executed. The ``__name__`` variable is local to every module and it is equal to @@ -137,19 +243,86 @@ Hence, all the code that goes in to the if block, ``if __name__ == "__main__":`` is executed only when the file is run as a python script. +.. L20 + +.. L21 + {{{ Show summary slide }}} -This brings us to the end of the tutorial. -we have learnt +.. R21 + +This brings us to the end of the tutorial.In this tutorial, we have +learnt to, + + 1. Know what happens when we import a module. + #. Use a script as a module. + #. Write test functions using the ``__name__`` idiom. + +.. L22 + +{{{Show self assessment questions slide}}} + +.. R22 + +Here are some self assessment questions for you to solve + +1. Which of the following variables contains the locations to search for + python modules + + - sys.pythonpath + - sys.path + - os.pythonpath + - os.path + + +2. A module should contain only functions. + - True + - False + + +3. The script ``utils.py`` is in one of locations of PYTHONPATH and + contains the following code +:: + + def show(x): + print x + + show("Hello World") + + if __name__ == "__main__": + + show("Hello Test") + + How do you use the ``show`` function after doing ``import utils`` + + - utils.show("hey") + - show("hey") + - utils.py.show("hey") + - utils.py.show.py("hey") + +.. L23 + +{{{solution of self assessment questions on slide}}} + +.. R23 + +And the answers, + +1. ``sys.path`` contains the locations to search for python modules. + +2. False. A module can contain a wide range of functions. + +3. After doing ``import utils``, we can use the function ``show()`` as, +:: + + utils.show("hey") - * What happens when we import a module - * How to use a script as a module - * How to write test functions using the __name__ idiom +.. L24 -{{{ Show the "sponsored by FOSSEE" slide }}} +{{{ Show the Thank you slide }}} -This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India +.. R24 -Hope you have enjoyed and found it useful. +Hope you have enjoyed this tutorial and found it useful. Thank you! |