python variables, functions, files for beginners @pyladies-berlin

intro-python.py

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# Python basics (Learning python the hard way 1-20)
# We will talk about:
#        * variables
#        * functions
#        * files
# by Mei Li Triantafyllidi
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# This presentation is executable python code
# Whatever is after # symbol is a comment
# the rest is code
# opensource presentation tool: 
#     https://github.com/inglesp/prescons
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# Variables
# ... are placeholders for data
# ... are symbolic names for values
x = 3
x
name = "Mary"
name

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# Python is strongly typed
# ... every variable has a type 
type(x)
type(name)

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# Python does dynamic typing
# ... the type of every variable can change
x = "a sequence of characters is a *string*"
type(x)

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# A variable can be assigned to an expression
k = 4
k = 3 + 5
k
k = 4*8.3 - 5
k
# expressions can include other variables
x = 3
z = 2*x + 5
# how much is z?
z

# what happens if we change x?
x = 4
# how much is z?
z

##########################################################
## What if we wanted z variable to change when we change x?
## --> Functions
## pieces of code that are defined in one place and executed in another
# Lets see a function example

def kelvin(celsius):
	kelvin_value = celsius + 273
	return kelvin_value
	
## ... then when we need to do the calculation
kelvin(54) # calling the function kelvin with parameter 54
kelvin_value = kelvin(21)
kelvin_value

# Another function example

def get_pyladies_link(location):
	return "http://" + location + ".pyladies.com"

get_pyladies_link("nyc")
site = get_pyladies_link("berlin")
site

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### Printing
### If you are not using the interactive console 
### the result of an expresion will not printed
### you have to use print python builtin function
print "Hello world!!!"

print "You can find our website at " + site + " stay in touch"

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### ... so far
### Variables store values:
###    - numbers (integers, real)
###    - strings (sequence of characters, text)
###    - ... lists, dictionaries, tuples, objects
### Variables get assigned to expressions
### Expressions can include
### * arithmetic operations between:
###   numbers, strings, variables, function calls
###   of similar type
###   ... logic operations 

intro = "This is pyladies site: " + get_pyladies_link("berlin")
intro


################################################
### ....lets continue with functions
### Functions can get more than one argument
### Fuctions do not need to return something

def greeting(name, site):
	print "Welcome " + name + "!!!"
	print "We are so happy to expand our community in " + site + "."
	
greeting("Helen", "http://best-site.com")

greeting("Korina", get_pyladies_link("berlin"))

##########################################################
## Functions summary
## * def is used to define the function
## * after is the function name
## * after the parameters comma separated in parenthesis (zero or more) 
## * return statement can used to return the outcome of the function

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## Files
## Writing to a file
filename = "myfirst_created_by_program_file.txt"

## function open
## http://docs.python.org/2/tutorial/inputoutput.html#reading-and-writing-files

f = open(filename, "w")
f.write("I can write in the file?!?!?!?")
f.close()

################################################
# Altogether
# Lets make a function to send greetings to some pyladies

def make_greeting_file(name):
	f = open("Greeting_" + name + ".txt", "w")
	f.write("Welcome " + name + "!!!\n")
	f.write("We are so happy to expand our community in pyladies.")
	f.close()

make_greeting_file("Marina")

# code reuse
make_greeting_file("Klara") 

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### Files summary

### * Files open with *open* function 
### * to open for writing, pass "w" as second parameter to open
### - Always close the file, with close method
### - use "write" method to write into a file
###
###  The end .... 
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