python learning notes

http://learnpython.org/

echo floating point with 4 digits, “argument specifier”

f=3.3465922378323784
print "%.4f" % f

This should also round corectly, giving 3.3466

functions

# function
def sum_two_numbers(a, b):
    return a + b

# call
x = sum_two_numbers(1,2)
print x

a placeholder pass

def somefunc():
    pass #this is a null statement/placeholder    

Can I have functions at the bottom of the script?

As sort of the gosub old basic approach

def main():
    # my code

def other()
    ....

def another()
    ....

def andmore()
    ....

main()

People say yes.

objects

# Objects are an encapsulation of variables and functions into a single entity. Objects get their variables and functions from classes. Classes are essentially a template to create your objects. 

class MyClass:
    variable = "blah"

    def function(self):
        print "This is a message inside the class."

# define object
myobjectx = MyClass()    # assign the above class(template) to an object 
print myobjectx.variable # the variable inside of the newly created object "myobjectx"

# another object of the same class
myobjecty = MyClass()
myobjecty.variable = "yackity" # change variable
print myobjecty.variable

dictionaries

phonebook = {
    "John" : 938477566,
    "Jack" : 938377264,
    "Jill" : 947662781
}

# write your code here
phonebook["Jake"] = 938273443
del phonebook["Jill"]

# testing code
if "Jake" in phonebook:
    print "Jake is listed in the phonebook."
if "Jill" not in phonebook:
    print "Jill is not listed in the phonebook."

modules

http://www.learnpython.org/en/Modules_and_Packages

import urllib
# which functions are implemented in each module
dir(urllib)
# When we find the function in the module we want to use, we can read about it more using the help function, inside the Python interpreter
help(urllib.urlopen)

lost

In this exercise, you will need to print an alphabetically sorted list of all functions in the re module, which contain the word find

import re

# Your code goes here
find_members = []
for member in dir(re):
    if "find" in member:
        find_members.append(member)

print sorted(find_members)

find_members is a list type of structure (something similar to array) and sorted is a sorting thing (function).

So if i say

somelist = [9,8,7]
print sorted(somelist)
# [7, 8, 9] < should happen

List Comprehensions

Using a list comprehension, create a new list called “newlist” out of the list “numbers”, which contains only the positive numbers from the list, as integers.

After quite some trouble I got this

numbers = [34.6, -203.4, 44.9, 68.3, -12.2, 44.6, 12.7]
newlist = []

for stuff in numbers:
    
    #print stuff
    stuff = int(stuff)
    
    if stuff > 0: # this should probably be if 'stuff >= 0:'
        newlist.append(stuff)
    
print newlist

which does work, but the official solution is this 3 liner

numbers = [34.6, -203.4, 44.9, 68.3, -12.2, 44.6, 12.7]
newlist = [int(x) for x in numbers if x > 0] # < what is this? Yeah that is an actual 'List Comprehension'
print(newlist)

About printf style formatting

# example
print "Result: %d" % result

https://en.wikipedia.org/wiki/Printf_format_string

The % results part seems to be called ‘string interpolation’.

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