Python Refresh
Keys in ___ are unique and immutable.
Dictionary
___ items are presented in key:value pairs, and can be referred to by using the key name.
Dictionary
____ is a collection which is ordered*, changeable and do not allow duplicates.
Dictionary
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[:] Result: [0, 1, 2, 3, 4, 5] Explanation: Omitting both start and stop returns the entire list.
Entire List With Full Slice
price = 49 txt = "The price is {} dollars"print(txt.format(price))
Add a placeholder where you want to display the price
Slicing
Allows access to a portion of a sequence type (string, list, tuple).
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[1:4] Result: [1, 2, 3] Explanation: Slices from index 1 up to, but not including, index 4.
Basic Slicing
del p1
Delete objects
del p1.age
Delete properties on objects
Example: my_string = "Hello World" Slicing: my_string[6:11] Result: "World" Explanation: Works the same as list slicing, but with string characters.
Slicing Strings
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[-5:4] Result: [1, 2, 3] Explanation: Combining negative and positive indices in slicing.
Slicing With Negative Start and Positive Stop
Example: my_tuple = (0, 1, 2, 3, 4, 5) Slicing: my_tuple[2:5] Result: (2, 3, 4) Explanation: Tuples can be sliced like lists, but the result is also a tuple.
Slicing With Tuples
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[-4:-1] Result: [2, 3, 4] Explanation: Negative indices count from the end of the list.
Slicing: Negative Indices
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[::-1] Result: [5, 4, 3, 2, 1, 0] Explanation: A negative step reverses the list.
Slicing: Negative Step
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[:3] Result: [0, 1, 2] Explanation: Omitting the start begins the slice from index 0.
Slicing: Omitting Start and Stop
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[3:] Result: [3, 4, 5] Explanation: Omitting the stop extends the slice to the end of the list.
Slicing: Omitting Stop
Example: my_list = [0, 1, 2, 3, 4, 5] Slicing: my_list[1:5:2] Result: [1, 3] Explanation: The step parameter skips elements in the specified range.
Slicing: Step Parameter
continue
Stop the current iteration, and continue with the next
break
Stop the loop even if the while condition is true:
Create a object
p1 = MyClass() print(p1.x)
How to avoid error if class is empty?
pass
Python built-in none type?
NoneType
List Comprehensions
Provide a concise way to create lists
Which set considered 'True/False' and '1/0' respectively, as the same values?
Set
___ is a collection which is unordered, unchangeable*, and unindexed. * Note: ___ items are unchangeable, but you can remove items and add new items.
Set
Which collection data type does not allow duplicates?
Set, Dictionary
x = True
Setting the Data Type: Bool
x = b"Hello"
Setting the Data Type: Bytes
x = bytearray(5)
Setting the Data Type: Bytesarray
x = {"name" : "John", "age" : 36}
Setting the Data Type: Dict
x = ["apple", "banana", "cherry"]
Setting the Data Type: List
x = {"apple", "banana", "cherry"}
Setting the Data Type: Set
x = ("apple", "1", "3.14")
Setting the Data Type: Tuple
iterable[start:stop:step]
Slicing
___ items are ordered, unchangeable, and allow duplicate values.
Tuple
Use ___ for data that shouldn't change through the course of a program.
Tuples
Reverses the order of the list
list.reverse()
Sorts the list
list.sort(reverse=True|False, key=myFunc) * reverse option. True will sort the list descending. Default is reverse=False * key optional. A function to specify the sorting criteria(s)
for x in fruits
loop each elem in list
for x in "banana"
loop through the characters in string
All classes have a function called ____, which is always executed when the class is being initiated.
__init__() function
Use the_____ to assign values to object properties, or other operations that are necessary to do when the object is being created:
__init__() function
class Person: def _____(self, name, age): self.name = name self.age
__init__() function
If the ____ is not set, the string representation of the object is returned:
__str__() function
The _____ controls what should be returned when the class object is represented as a string.
__str__() function
class Person: def __init__(self, name, age): self.name = name self.age = age def _____(self): return f"{self.name}({self.age})"p1 = Person("John", 36)print(p1)
__str__() function
list.append(elmnt)
add an elem to the end of the list.
for x in cars:
'For in' loop to loop through all the elements of an array
What does find() return if value is not found?
-1
x = cars[0]
Get value of first elem in array
x = 5 print(type(x))
Getting the Data Type
Tuple
Immutable sequences, typically used to store collections of heterogeneous data.
"".join(iterable)
Joins the elements of an iterable to the end of the string
___ items are ordered, changeable, and allow duplicate values.
List
[x for x in iterable] or can include conditions: [x for x in iterable if condition]
List Comprehensions
___ are dynamic and can contain mixed data types.
Lists
p1.age = 40
Modify properties on objects
cars[0] = "Toyota"
Modify value of first elem in array
List
Mutable sequences, typically used to store collections of homogeneous items.
Python built-in binary type?
bytes, bytearray, memoryview
Add elem to an array
cars.append("Honda")
Remove elem in array and return it
cars.pop(1) # second elem position
Remove elem in array and do not return in
cars.remove("Volvo") Note: only removes the first occurrence of the specified value.
Create a class
class MyClass: x = 5
Python built-in mapping type?
dict
x = constructor(name = "John", age = 36, country = "Norway") print(x)
dict() constructor
f'Hello, {name}'
formating a string
What is the difference between find() and index()?
index() method raises an exception if the value is not found.
Python built-in numeric type?
int, float, complex
Python built-in sequence type?
list, tuple, range
Removes all the elements from the list
list.clear()
Returns a copy of the list
list.copy()
Returns the number of elements with the specified value
list.count(value)
Add the elements of a list (or any iterable), to the end of the current list
list.extend(iterable)
Returns the index of the first element with the specified value
list.index(elmnt)
Adds an element at the specified position
list.insert(pos, elmnt)
Returns a reversed iterator object.
reversed(sequence)
The ____ parameter is a reference to the current instance of the class, and is used to access variables that belong to the class.
self
Python built-in set type?
set, frozenset
Python built-in text type?
str
Method to return the number of times a defined value appears in the string:
string.count(value, start, end) ** value required
Returns true if the string ends with the specified value
string.endswith(value, start, end) * start optional * end optional
Method to find the first occurrence of the specified value.
string.find(value, start, end) ** value required
Converts a string into lower case
string.lower()
Returns a string where a specified value is replaced with a specified value
string.replace(oldvalue, newvalue, count) * old value required * new value required
Splits the string at the specified separator, and returns a list
string.split(separator, maxsplit) * separator optional * maxsplit optional
Splits the string at line breaks and returns a list
string.splitlines(keeplinebreaks) * keeplinebreaks option. default value is false
Returns true if the string starts with the specified value
string.startswith(value, start, end) * start optional * end optional
Returns a trimmed version of the string
string.strip(characters) * characters option
Converts a string into upper case
string.upper()
Dictionary
used to store key-value pairs and are optimized for retrieving data.
How do I create a tuple with one item?
x = ("apple",)