Python Notes Flashcards
Is python case sensitive and does spacing matter?
yes to both
What is Print used for?
To show a value
Arithmatic in python?
+, -. *, /
Addition, subtraction, multiplication, division
**?
Does number to the power of a other
what does % do?
Gives remainder from a division
//?
Divides one number by another but rounds down to nearest integer
(still rounds down even when negative)
how to assign closely related variables?
x, y, z = 2, 3, 4
Can you have spaces in variable names?
no, should use underscores and all lower case
what is += used for?
Telling a descriptive value it is being effected by new values
also -= when want to subtract values
Float?
Decimal answer (even if it .0
Int?
Integer (whole number)
How to find out if int or float?
Use type()
Interaction with an int and a float always =?
Float
Can also use int and float as functions to add or remove decimal points
x = int(4.7) # x is now an integer 4
y = float(4) # y is now a float of 4.0
What does bool (boolean) do?
Say if something is true or false
Comparison operators?
< less than
> greater than
<= less or equal than
>= greater or equal than
== equal to
!= not equal to
What is a string?
Data type for immutable ordered sequences of characters
How to print words?
Use Print (“…….”)
How to get rid of issue of using speech marks within a quote?
Use single for overall one, and use double for quote
If need more than one, use a / before the ‘ to let python know its part of the string
How to combine, or repeat strings or put a space?
+ for combine
- for repeat
” “ for space
what does Len( ) do?
Returns the length of a string
How to convert values into a string value?
str()
How to convert values into a integer?
Int()
What is a method?
A function that belongs to an object
for example title() will turn the string into a title so capitals in each words
Is placed in the bracket and doesn’t need anything in its own brackets, acts on the string
What is the length of the string variable verse?
What is the index of the first occurrence of the word ‘and’ in verse?
What is the index of the last occurrence of the word ‘you’ in verse?
What is the count of occurrences of the word ‘you’ in the verse?
length = len(verse)
print(length)
index = verse.index(“and”)
print(index)
rindex = verse.rindex(“you”)
print(rindex)
count = verse.count(“you”)
print(count)
Example of a list and how to access parts of the list?
months = [‘January’, ‘February’, ‘March’, ‘April’, ‘May’, ‘June’, ‘July’, ‘August’, ‘September’, ‘October’, ‘November’, ‘December’]
print(months[0]) # January
print(months[1]) # February
print(months[7]) # August
print(months[-1]) # December
print(months[25]) # IndexError: list index out of range
How would you get the Q3 months (slicing)
months = [‘January’, ‘February’, ‘March’, ‘April’, ‘May’, ‘June’, ‘July’, ‘August’, ‘September’, ‘October’, ‘November’, ‘December’]
q3 = months[6:9]
print(q3) # [ ‘July’, ‘August’, ‘September’]
Note how the lower bound is inclusive, but the upper bound is exclusive
Note it starts from 0, not 1
What do ‘in’ and ‘not in’ do?
evaluates if the object on the left hand side is in, or not in the object on the right eg.
eg . print( ‘Sunday’ in months, ‘Sunday’ not in months)
Gives False True
Difference between strings and lists?
Mutability is whether an object can change its values once it has been created
Lists are mutable (can be changed)
Strings are immutable (can’t be changed)
What is ordering and are lists and strings ordered?
When order of elements within a list matter
Yes both strings and lists are ordered
Use list indexing to determine how many days are in a particular month based on the integer variable month, and store that value in the integer variable num_days. For example, if month is 8, num_days should be set to 31, since the eighth month, August, has 31 days.
month = 8
days_in_month = [31,28,31,30,31,30,31,31,30,31,30,31]
num_days = days_in_month[month - 1]
print(num_days)
what does max() do when used on a list or string?
Gives the largest value
Value that would appear last if ordered alphabetically
What does min() do?
Opposite of max
What does sorted() do?
Returns a copy of a list ordered from smallest to largest, leaving the original unchanged
can do the opposite argument by adding into the function ,reverse=true
How to separate all the words out in a list on separate lines?
“/n”.join
if want hypothons between the words use “-“ .join
Difference between data types and data structures?
A data type is just a type that classifies data. This can include primitive (basic) data types like integers, booleans, and strings, as well as data structures, such as lists.
Data structures are containers that organize and group data types together in different ways. For example, some of the elements that a list can contain are integers, strings, and even other lists!
What is a tuple?
A data type for immutable ordered sequences of elements
Used when have values that are so closely related will always be used together, eg longitude and latitude
Example of a tuple?
dimensions = 52, 40, 100
length, width, height = dimensions
print(“The dimensions are {} x {} x {}”.format(length, width, height))
What are sets?
A data type for mutable unordered collections of unique elements
eg. amount of people visiting your website and you collect all the countries it has been from, there will be duplicates
How do you remove duplicates?
Use the set() function
countries = [‘Angola’, ‘Maldives’, ‘India’, ‘United States’, ‘India’, ‘Denmark’, ‘Sweden’, ‘Ghana’, … 777 more countries not displayed]
print(len(countries)) # 785
print(countries[:5]) # [‘Angola’, ‘Maldives’, ‘India’, ‘United States’, ‘India’]
country_set = set(countries)
print(country_set) = 196
What does the add() and pop() methods do?
You can add elements to sets using the add method, and remove elements using the pop method, similar to lists. Although, when you pop an element from a set, a random element is removed. Remember that sets, unlike lists, are unordered so there is no “last element”.
Whats a dictionary?
A data type for mutable objects that store mappings of unique keys to values
eg. elements = {“hydrogen”: 1, “helium”: 2, “carbon”: 6}
What does get() do?
Sees if value is in a dictionary, gives true or false
Example of identity operators?
is evaluates if both sides have the same identity
is not - evaluates if both sides have different identities
Example of a compound data structure, what does it add to the elements table?
elements = {“hydrogen”: {“number”: 1,
“weight”: 1.00794,
“symbol”: “H”},
“helium”: {“number”: 2,
“weight”: 4.002602,
“symbol”: “He”}}
How do you do a lookup in a compound data structure?
helium = elements[“helium”] # get the helium dictionary
hydrogen_weight = elements[“hydrogen”][“weight”] # get hydrogen’s weight
How do you add to a compound data structure?
oxygen = {“number”:8,”weight”:15.999,”symbol”:”O”} # create a new oxygen dictionary
elements[“oxygen”] = oxygen # assign ‘oxygen’ as a key to the elements dictionary
print(‘elements = ‘, elements)
How do you split a verse into a list of words?
verse_split = verse.split()
How do you turn a list of words into a data structure that stores unique elements?
verse_set = set(verse_list)
How do you count the amount of words in a unique data structure?
num_unique = len(verse_set)
How do you find if a certain word is in the dictionary?
contains_breathe = if ‘breathe’ in verse_dict:
print(“The word ‘breathe’ is in the dictionary.”)
else:
print(“The word ‘breathe’ is not in the dictionary.”)
print(contains_breathe)
How do you find the unique number of keys in a dictionary?
num_keys = len(verse_dict.keys())
print(num_keys)
How do you create and sort a list of dictionary keys?
sorted_keys = sorted(verse_dict.keys())
How do you find the first element in the dictionary keys?
first_key = sorted_keys[0]
print(first_key)
How do you find the element with the highest value in the list of keys?
key_with_highest_value = max(verse_dict, key=verse_dict.get)
print(key_with_highest_value)
Features of a list?
Ordered
Mutable
[ ] or list() - are its constructors
eg. [5.7, 4, ‘yes’, 5.7]
Features of a tuple?
Ordered
Not Mutable
( ) or tuple() are its constructors
eg. (5.7, 4, ‘yes’, 5.7)
Features of a set?
Not ordered
Mutable
{}* or set() are its constructors
eg. {5.7, 4, ‘yes’}
Features of a dictionary?
Not ordered
Not mutable
{ } or dict() are its constructors
eg. {‘Jun’: 75, ‘Jul’: 89}
