https://www.geeksforgeeks.org/differences-and-applications-of-list-tuple-set-and-dictionary-in-python/

Python Data Structures

List [1,2,3,4,5]

• like an array
• allow duplicates

Tuple (1,2,3,4,5)

• more like an array of constants
• allow duplicate elements

Dictionary {1:"a", 2:"b"}

• ordered key-value pairs
• does not allow duplicate keys

Set {1,2,3,4,5}

• will not allow duplicate elements

if __name__=='__main__'

• this code only gets run if this file is executed directly and not used in an import

Keyword arguments

def add_suffix(suffix='.com'):

**kwargs - keyword arguments

def convert_and_sum_list_kwargs(usd_list, **kwargs):

• can be accessed as a dictionary
• commonly used when passing to another function

using % in a string

name = "Geek"

append a string within a string

print("Hey, %s!" % name)

scope

• use the global keyword to use globals global score
• • use the nonlocal to get it from the scope above nonlocal score

lambdas

```add_up = lambda x, y: x + y print(add_up(2, 5))

### mapping with lambdas
* first argument is function to apply
* second is an iterable

```lengths = list(map(len, names)```
* (map returns a generator)

# generator
a function which uses yield to return a series of results which change each time it is called

## filter() is similar - takes a function and an iterable
```names = ['Josefina', 'Jim', 'Kim']
list(filter(lambda name: len(name) == 3, names))

and sorted()

names = ['Ming', 'Jennifer', 'Andrew', 'Boris']
sorted(names, key=lambda x : len(x))

Objects

view properties and methods

## Classes

class Australian is_human = True enjoys_sport = True

john = Australian() type(John) john.is_human

### Constructors

def init(self, height): self.height = height

### To get attributes of object:
```usa.__dict__```

## Methods
### Instance

def area(self):

### Static

@staticmethod def format_date(date): #can only access what is passed

### Class - can be used to instantiate
can access class level variables

@classmethod def is_sporty_human(cls):

### The str method - when you print(instance)

def str(self):

## The property decorator

@property def fahrenheit(self): return self.celsius * 9 / 5 + 32

Can now use this as an attribute:

freezing.fahrenheit #do need for ()

## The setter method - update multiple attributes simultaneously

@full_name.setter def full_name(self, name): first, last = name.split(‘ ‘) self.first_name = first self.last_name = las

*Can also be used for validation* (ValueError?)

## Inheritance

class Pet: def init(self, name, weight): self.name = name self.weight = weight

class Cat(Pet) is_feline = True

## Overridding



## Calling the parent method with super()

super().speak()

# The Standard Library
## Working with dates and times


## Dates and Times

from datetime import date, time, datetime
date(year=2020, month=1, day=31)
# datetime.date(2020, 1, 31)

time(hour=13, minute=14, second=31)
#datetime.time(13, 14, 31)

datetime(year=2020, month=1, day=31, hour=13, minute=14, second=31)
# datetime.datetime(2020, 1, 31, 13, 14, 31) ```

date.today()
datetime.now()
datetime.combine()
date.fromisoformat("2020-01-31")

Can use srtptime for different formats:

date_string = "01-31-2020 14:45:37"
format_string = "%m-%d-%Y %H:%M:%S"
datetime.strptime(date_string, format_string)

Working with time zones

• datetime provides tzinfo
• allows datetime.datetime and datetime.time to include timezones information
• also need python-dateutil

from dateutil import tz
from datetime import datetime

now = datetime.now(tz=tz.tzlocal())
now
datetime.datetime(2020, 1, 26, 0, 55, 3, 372824, tzinfo=tzlocal())
now.tzname()
'Eastern Standard Time'

Using collections in Python

The counter class

• counts hashable objects
• has keys and values

Counter('abracadabra').most_common(3)

The defaultdict class

• defaultdict is a Python type that inherits from dict:

def_dict = defaultdict(list)  # Pass list to .default_factory
def_dict['one'] = 1  # Add a key-value pair

The ChainMap class

functools