Python Basics

Question 1

2 types of functions?

Answer 1

built in functions and custom made

Question 2

how to create function

Answer 2

define it.
def functionname(arguments).

Question 3

function

Answer 3

function is some stored code we use. we take some input and create output

Question 4

implicent

Answer 4

when you multipy int and float in implicently becomes float.

Question 5

converting datatypes

Answer 5

newint = int(oldval)

cant convert string to inv if not number

Question 6

function

Answer 6

def print_lyrics():
    print ("I'm a lumberjack, and I'm okay.”)
    print ('I sleep all night and I work all day.’)

Question 7

function argument

Answer 7

An argument is a value we pass into the function as its input when we call the function
We use arguments so we can direct the function to do different kinds of work when we call it at different times
We put the arguments in parentheses after the name of the function

Question 8

parameter

Answer 8

A parameter is a variable which we use in the function definition. It is a “handle” that allows the code in the function to access the arguments for a particular function invocation.
lang is the parameter.

Question 9

return

Answer 9

Often a function will take its arguments, do some computation, and return a value to be used as the value of the function call in the calling expression. The return keyword is used for this.

Question 10

return is

Answer 10

A “fruitful” function is one that produces a result (or return value)
The return statement ends the function execution and “sends back” the result of the function

Question 11

parameter order and number

Answer 11

We can define more than one parameter in the function definition
We simply add more arguments when we call the function
We match the number and order of arguments and parameters

Question 12

void

Answer 12

When a function does not return a value, we call it a “void” function
Functions that return values are “fruitful” functions
Void functions are “not fruitful”

Question 13

what is a list?

Answer 13

A List is a kind of Collection.
A collection allows us to put many values in a single “variable”
A collection is nice because we can carry all many values around in one convenient package.

Question 14

describe list

Answer 14

List constants are surrounded by square brackets and the elements in the list are separated by commas
A list element can be any Python object - even another list
A list can be empty
.
print ([1, 24, 76])
[1, 24, 76]
>>> print (['red', 'yellow', 'blue’])
['red', 'yellow', 'blue']
>>> print(['red', 24, 98.6])
['red', 24, 98.6]
>>> print([ 1, [5, 6], 7])
[1, [5, 6], 7]
>>> print([])
[]

Question 15

simple for loop examples

Answer 15

friends = [‘Joseph’, ‘Glenn’, ‘Sally’]
for friend in friends :
print(‘Happy New Year:’, friend)
print(‘Done!’)

z = [‘Joseph’, ‘Glenn’, ‘Sally’]
for x in z:
print(‘Happy New Year:’, x)
print(‘Done!’)

Question 16

ping element

Answer 16

friends = [ ‘Joseph’, ‘Glenn’, ‘Sally’ ]
»> print(friends[1])
Glenn

Question 17

strings vs list

Answer 17

Strings are “immutable” - we cannot change the contents of a string - we must make a new string to make any change
Lists are “mutable” - we can change an element of a list using the index operator
fruit = 'Banana'
>>> fruit[0] = ‘b'
Traceback 
lotto[2] = 101
>>> print (lotto) 
[2, 14, 101, 41, 63]

Question 18

len() function

Answer 18

The len() function takes a list as a parameter and returns the number of elements in the list
Actually len() tells us the number of elements of any set or sequence (such as a string...)
>>> greet = 'Hello Bob'
>>> print (len(greet))
9
>>> x = [ 1, 2, 'joe', 99]
>>> print (len(x))
4

Question 19

range()

Answer 19

The range function returns a list of numbers that range from zero to one less than the parameter
We can construct an index loop using for and an integer iterator
»> print (range(4))
[0, 1, 2, 3]
»> friends = [‘Joseph’, ‘Glenn’, ‘Sally’]
»> print (len(friends))
3
»> print (range(len(friends)))
[0, 1, 2]
»>

Question 20

2 more loop examples using range/len and for

Answer 20

friends = [‘Joseph’, ‘Glenn’, ‘Sally’]

for friend in friends :
print (‘Happy New Year:’, friend)

for i in range(len(friends)) :
friend = friends[i]
print (‘Happy New Year:’, friend)

Question 21

add lists togeter

Answer 21

We can create a new list by adding two existing lists together
a = [1, 2, 3]
>>> b = [4, 5, 6]
>>> c = a + b
>>> print (c)
[1, 2, 3, 4, 5, 6]
>>> print (a)
[1, 2, 3]

Question 22

more list functions

Answer 22

List.count(element)
List.insert (index, element)
List. append(new element) #appends an element to the end of the list
List.remove(element)
List.sort()
del list[index]

Question 23

show list functions

Answer 23

a = [66.25, 333, 333, 1, 1234.5] # create a list
print a.count(333), a.count(66.25), a.count(‘x’)

a.insert(2, -1) #List.insert(index, element)
a.append(333) # appends an element to the end of the list.
a

a.index(333) #show the first found element’s index
a.remove(333) # removes first found elements of the same value.
a

a.sort()# ascending order. If its list of strings, it will show in alphabetically order.
a

a.pop()#list.pop(pos) pos needs to be a specified position that you want to remove. If no input of pos, then remove the last element.
a

Question 24

list vs. dictionary

Answer 24

List
- A linear collection of values that stay in order

Dictionary
- A “bag” of values, each with its own label

Question 25

Dictionaries

Answer 25

Dictionaries are Python’s most powerful data collection
Dictionaries allow us to do fast database-like operations in Python
Dictionaries have different names in different languages
- Associative Arrays - Perl / PHP
- Properties or Map or HashMap - Java
- Property Bag - C# / .Net

Question 26

describe picture of dictionary statement

Answer 26

Construct dictionary
food={‘ham’: ‘yes’, ‘egg’: ‘yes’}
a = dict(one=1, two=2, three=3) #use dict() function
We can use any types as value but no lists or dictionaries can be used for keys.
Use [key] to index the entries
»>food[‘ham’]
‘yes’
Add new element:
»>food[’spam’]=‘no’
»>food
food = {“ham” : “yes”, “egg” : “yes”, “spam” : “no” }

Question 27

change value of dictionary

Answer 27

Change the value
»> food = {“ham” : “yes”, “egg” : “yes”, “spam” : “no” }
»> food
{‘egg’: ‘yes’, ‘ham’: ‘yes’, ‘spam’: ‘no’}
»> food[“spam”] = “yes”
»> food
{‘egg’: ‘yes’, ‘ham’: ‘yes’, ‘spam’: ‘yes’}

Question 28

copy and merge dictionary.

Answer 28

A dictionary can be copied
food={'ham': 'yes', 'egg': 'yes'}
w=food.copy()
Clean
>>> w.clear()
>>> print w
{}
Merging 
>>> w={"house":"Haus","cat":"Katze","red":"rot”}
>>> w1 = {"red":"rouge","blau":"bleu"}
>>> w.update(w1)
>>> print w
{'house': 'Haus', 'blau': 'bleu', 'red': 'rouge', 'cat': 'Katze'}

Question 29

dif between list and dict

Answer 29

lst = list()
>>> lst.append(21)
>>> lst.append(183)
>>> print (lst)
[21, 183]
>>> lst[0] = 23
>>> print(lst)
[23, 183]
ddd = dict()
>>> ddd['age'] = 21
>>> ddd['course'] = 182
>>> print(ddd)
{'course': 182, 'age': 21}
>>> ddd['age'] = 23
>>> print(ddd)
{'course': 182, 'age': 23}

Question 30

find something in dict

Answer 30

It is an error to reference a key which is not in the dictionary
We can use the in operator to see if a key is in the dictionary
>>> ccc = dict()
>>> print(ccc['csev'])
Traceback (most recent call last):
  File "", line 1, in 
KeyError: 'csev'
>>> 'csev' in ccc
False

Question 31

gets method

Answer 31

We can use get() and provide a default value of zero when the key is not yet in the dictionary - and then just add one
Counts = dict()
Names = [‘bush’, ‘cwen’, ‘zhen’, ‘raja’, ‘cwen’, ‘raja’]
for name in Names :
Counts[name] = Counts.get(name, 0) + 1
print(counts)

Question 32

count words.

Answer 32

counts=dict()
A = raw_input(‘Please enter a line of text: ‘)

words = A.split()

print ‘Words:’, words

print ‘Counting…’
for word in words:
counts[word] = counts.get(word,0) + 1
print counts

Question 33

why numpy?

Answer 33

ndarray: vectorized arithmetic operations and broadcasting capabilities
Standard mathematical functions for fast operations on entire arrays of data. No need to write loops.
Tools for reading/writing array data
Linear algebra, random number generation and so on

Question 34

how does mapreduce work?

Answer 34

MapReduce works by breaking the processing into two phases: the map phase and
the reduce phase. Each phase has key-value pairs as input and output, the types of
which may be chosen by the programmer. The programmer also specifies two
functions: the map function and the reduce function.