Intermediate Python.pdf

- l.pop(3) removes and returns the fourth item
- l.remove(x) removes the first item equal to x
- l.reverse() reverses the order
- l[1::2] returns every second item
- l[-5:] returns the last 5 items

STRINGS:
- s.lower() returns lowercase
- s.title() capitalizes the first letter of each word
- "23".zfill(4) left-fills with 0's to length 4
- s.splitlines() splits on newline characters
- s[:5] returns the first 5 characters
- "fri" + "end" returns "friend"
- "end" in s checks for substring

RANGE:
- range(5) returns a sequence from 0 to 4
- range(2000,2018) returns a sequence from 2000 to 2017
- range(0,11,2) returns a sequence from 0 to 10, incrementing by 2
- range(0,-10,-1) returns a sequence from 0 to -9
- list(range(5)) returns a list from 0 to 4

DICTIONARIES:
- max(d, key=d.get) returns the key with the largest value
- min(d, key=d.get) returns the key with the smallest value

SETS:
- myset = set(l) returns a set with unique values from l
- len(myset) returns the number of unique values
- a in myset checks for value existence

REGULAR EXPRESSIONS:
- re.search("abc",s) returns a match object if "abc" is found
- re.sub("abc","xyz",s) replaces "abc" with "xyz"

LIST COMPREHENSION:
- [i 2 for i in range(10)] returns squares of values from 0 to 9
- [s.lower() for s in lstrings] applies .lower() to each item
- [i for i in lfloats if i < 0.5] returns items less than 0.5

FUNCTIONS FOR LOOPING:
- for i, value in enumerate(l) iterates over index and value
- for one, two in zip(lone,ltwo) iterates over two lists
- while x < 10 runs code until x is no longer less than 10

DATETIME:
- import datetime as dt imports the datetime module
- now = dt.datetime.now() gets the current time
- wks4 = dt.datetime.timedelta(weeks=4) represents a 4-week timespan
- now - wks4 returns the time 4 weeks prior
- newyear2020 = dt.datetime(year=2020, month=12, day=31) represents December 31, 2020
- newyear2020.strftime("%A, %b %d, %Y") formats the datetime
- dt.datetime.strptime('Dec 31, 2020',"%b %d, %Y") parses a datetime string

RANDOM:
- import random imports the random module
- random.random() returns a random float between 0.0 and 1.0
- random.randint(0,10) returns a random integer between 0 and 10
- random.choice(l) returns a random item from the list

COUNTER:
- from collections import Counter imports the Counter class
- c = Counter(l) counts unique items
- c.mostcommon(3) returns the 3 most common items

TRY/EXCEPT:
- try/except blocks catch and handle errors
- lints = [1, 2, 3, "", 5] demonstrates error handling with missing values
- lfloats = [] and the for loop convert values to float, handling ValueError