I am paid to write programs and have been since 1979
including programming python

the standard template I use when starting a new program is


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def	run():
# do stuff here	
	
if __name__ == '__main__':
	run()

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I suggest you do the same


Python programs consist of modules.
A module is a .py file  (more or less)

A lot of python is written in python as modules
so you standard template might easily become
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import 	os
import	sys


def	run():
# do stuff here	
	
if __name__ == '__main__':
	run()

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the reason for the
if __name__ == '__main__':
	run()
	
is the variable __name__ is set to '__main__'
if, and only if, the module is invoked from the  command line

python  my_module.py

it is possible to have code in a python file not in a function   e.g.

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print(' this message will be printed out whenever this module is loaded')
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the if __name__ == '__main__' is to ensure that the code is only run
if it's in the main module (i.e. the one mentioned on the command line)



functions enable your program to be split into small chunks
ideally each function should do a single task
this makes it easier to understand and check that it is right
in addition your function may be used by many different python programs (e.g. read a file)


Besides functions there are 2 main programming things (constructs)

Loops and if/elif/else 

loops allow a piece of code to be repeated over and over, while something changes
the 2 main mechanisms for loops in python are while and for

while  <condition>:
	statements
	
	
a <condition> is some logically test which might be as simple as
True  which is always true

or something like 
i < 10

e.g.
i = 0
while i < 10:
	print(i)
	i = i + 1
	
this will print out the numbers 0 to 9

a very common mistake in such a loop is to miss out 
i = i + 1

so the loop goes on for ever


there is an easier way to code this in python

for i in range(10):
	print(i)
	
here range ensures that  i is set from 0 to 9 in steps of 1

range takes up to three parameters 2 being optional

range( [start], stop, [step])

so to go from 1 to 11 in steps of 2
range(1, 12, 2)  # remember in python the end limit is 1 passed where you want to stop

Comments

# any character after a # is ignored until the start of a new line


Types

Python has different 'types' for data
'1'  is a string which holds the character 1
'hello samuel' is a longer string

1  is an integer.  Integers are whole numbers

1.0 is a float i.e. a decimal numbers


in python you create variables by assigning them a value e.g.

my_age = 62

my_first_name = 'Humperdink'

unlike languages like java or c++ you do not have to specify the type of variables in advance
AND
the type of a variable can change just by assigning something different to it

my_age = 62  # type of my_age is integer

my_age = 'little jim'  # type of my_age is now string



Classes

Enable you to create new types
but that is for another day



Collections

the main collections in pythons are
lists and dictionaries

a list is a collection of things, which can be all different types, though often not

If you read a file it is common to get a list of strings each 'element' in the list is a single line of the file.


a dictionary is a collection of key value pairs

e.g.

my_dict = {
			'samuel'	: 'Samuel Shiers',
			'alex		: 'Alexandra Shiers,
			'becca'		: 'Rebecca Shiers'
		}

you can test if a key exists in a dictionary

test_key = 'ethel'
if test_key in my_dict:
	print(my_dict[test_key])
else:
	print('{0} not in my_dict'.format(test_key)
	

	
Really there are 2 parts in learning to program

1)  practicing using building blocks (ie doodles) 
	such as reading a file

2)	when trying to write a problem seeing how the problem can be broken into building blocks
	and how these building blocks can be bolted together to make a program which solves the problem