Python

Question 1

Function Definition

Answer 1

def functionname():

  body

  return()

Question 2

Importing modules

Answer 2

Generic Import:

import modulename

use as: modulename.functionname()

Function Import:

from modulename import functionname

use as: functionname()

Universal Import:

from modulename import *

use as functionname()

Question 3

if statement

Answer 3

if x < 0:

  x = 0

  print 'Negative changed to zero'

elif x == 0:

  print 'Zero'

elif x == 1:

  print 'Single'

else:

  print 'More'

Question 4

List

Answer 4

Lists are a datatype you can use to store a collection of different pieces of information as a sequence under a single variable name. Index starts at Zero

• list_name* = [item_1, item_2]
• empty_list* = [].

Question 5

List - append function

Answer 5

list_name.append(new item)

append is a built-in function of lists, it appends a new item at the end of the list

Question 6

List - slicing

Answer 6

slice = list_name[first slice item index: last slice item index + 1: stride]

Question 7

strings - slicing

Answer 7

stringname[:3] - first 3 characters

stringname[3:5] - from fourth to fifth

stringname[3:] - from second to last

Question 8

List - index function

Answer 8

listname.index(itemname) will return the first index that contains the item. If there is no such item will return an error

Question 9

List - insert function

Answer 9

listname.insert(index,item) inserts item with specified index on listname

Question 10

for loop

Answer 10

for variable in list_name:

 # do stuff

 break

else:

# do other stuff 

A variable name follows the for keyword; it will be assigned the value of each list item in turn. in list_name designates list_name as the list the loop will work on. The line ends with a colon (:) and the indented code that follows it will be executed once per item in the list.

else statement is executed after the for loop ends, except when a break occurs

Question 11

List - sort function

Answer 11

listname.sort()

sorts listname in increasing order

Question 12

Dictionary - Definition

Answer 12

A dictionary is similar to a list, but you access values by looking up a key instead of an index. A key can be any string or number. Dictionaries are enclosed in curly braces, like so:

d = {‘key1’ : 1, ‘key2’ : 2, ‘key3’ : 3}

This is a dictionary called d with three key-value pairs. The key ‘key1’ points to the value 1, ‘key2’ to 2, and so on.

Question 13

List - Length function

Answer 13

len(listname)

returns the number of items on the list

Question 14

Dictionary - new entry

Answer 14

A new key-value pair in a dictionary is created by assigning a new key, like so:

dict_name[new_key] = new_value

An empty pair of curly braces {} is an empty dictionary, just like an empty pair of [] is an empty list.

Question 15

Dictionary - Length function

Answer 15

len(dictionary)

returns the number of pairs on the dictionary. Each pair counts only one, even if the value is a list

Question 16

Dictionary - del command and remove function

Answer 16

del dict_name[key_name]

will remove the pair with key_name from dict_name

my_list.remove(value)

will remove the the first item from my_list that has a value equal to value.

The difference between del and .remove() is: del deletes a key and its value based on the key you tell it to delete. .remove() removes a key and its value based on the value you tell it to delete

Question 17

range

Answer 17

A range can take 1, 2 or 3 arguments. If you use one argument, it starts the range at zero and increments by 1 until the size reaches 1 less than the range. For instance,

range(1) # => [0]

range(2) # => [0,1]

If you use two arguments, the first argument is the start for the range and the second argument is the same as above: range(1,3) # => [1,2]

If you use 3 arguments, the range’s first argument is the number the list starts at, the second number is where the list ends, and the third argument is how much you should increment by instead of the default increment of 1. For instance: range(2,8,3) # => [2,5] range(2,9,3) # => [2,5,8]

Question 18

while loop

Answer 18

while condition:

 #code to execute break statement will exit the loop

Question 19

while / else loop

Answer 19

while condition:

  code break else:

        code the else will execute when the while condition is not satisfied, and the loop ends. If the while exits because of a break statement then the else is not executed

Question 20

List - zip fuction

Answer 20

zip will create pairs of elements when passed two lists, and will stop at the end of the shorter list. zip can handle three or more lists as well

list_a = [3, 9, 17, 15, 19]
list_b = [2, 4, 8, 10, 30, 40, 50, 60, 70, 80, 90]

for a, b in zip(list_a, list_b):
if a>b: print a
else: print b

Question 21

Iterators for dictionaries

items(), keys() and values()

Answer 21

items() will iterate over a dictionary and return those key/value pairs

d = {
“Name”: “Guido”,
“Age”: 56,
“BDFL”: True
}

Calling:

d.items()

Will result in

=> [(‘BDFL’, True), (‘Age’, 56), (‘Name’, ‘Guido’)]

keys() function returns an array of the dictionary’s keys
values() function returns an array of the dictionary’s values.

Question 22

List comprehension

Answer 22

*new\_list* = [x for x in range(1,6)]
 # =\> [1, 2, 3, 4, 5]

doubles = [x\*2 for x in range(1,6)]
 # =\> [2, 4, 6, 8, 10]

list_name = [x*2 for x in range(1,6) if (x*2)%3 == 0]

=> [6]

Question 23

Lambda functions

Answer 23

lambda x: function based on x

Lambda is a shorthand to create anonymous functions y python

Question 24

Class - Basics

Answer 24

Class Syntax
 A basic class consists only of the class keyword, the name of the class, and the class from which the new class inherits in parentheses. (We'll get to inheritance soon.) For now, our classes will inherit from the object class, like so:

class NewClass(object):

  def \_\_init\_\_(self):

# Class magic here

This gives them the powers and abilities of a Python object. By convention, user-defined Python class names start with a capital letter.

Question 25

Class - __init()__ and self

Answer 25

You can think of __init__() as the method that “boots up” a class’ instance object: the init bit is short for “initialize.”

The first argument __init__() gets is used to refer to the instance object, and by convention, that argument is called self. If you add additional arguments—for instance, a name and age for your animal—setting each of those equal to self.name and self.age in the body of __init__() will make it so that when you create an instance object of your Animal class, you need to give each instance a name and an age, and those will be associated with the particular instance you create.

class Animal(object):
     def \_\_init\_\_(self, name, age):
         self.name = name
         self.age = age

zebra = Animal(“Jeffrey”, 2)
giraffe = Animal(“Bruce”, 1)

Question 26

Class - Scope