Basic Pythonic tricks

• like char b = ‘a’ + 1; in python b = chr(ord(a)+1).

Lists

    lis = [2,3,4,5,6,7]
    lis = [1] + lis + [8]
    # lis is now [1,2,3,4,5,6,7,8] 

    # flatten a grid
    [x for row in grid for x in row]

Sorting

    lis = [2,3,4,5,6,7]
    lis.sort() # returns nothing updates in-place
    lis.sort(key=abs, reverse=True) # descending order of absolute val

    sorted(lis, key=abs, reverse=True) # returns a copy leaves original as is

Set

element you add must be hashable; for ex. list = [] is not hashable so we do set.add(tuple(list()))

    myset = set()
    
    myset.add(1)
    myset.remove(2) # throws KeyError if 2 not present

    myset.union(otherSet)
    myset.intersection(otherSet)
    myset.difference(otherSet)
    
    myset.issubset(otherSet)
    myset.issuperset(otherSet)

Slicing

Often for string/array ops you may need to perform fancy iterations, tis always simpler to just be smart with slicing.

[start : stop : step]

for example, say you must reverse every k sized block for a list

    lis = [1,2,3,4,5,6,7,8,9,10]
    n = len(lis)
    assert k > 0
    for i in range(0,n,k):
        lis[i:i+k] = lis[i:i+k][::-1]
        # or just lis[i:i+k] = list(reversed(lis[i:i+k])) # reversed returns an iterator

Web Things

Often, someone would want you to quickly spin up a web-dih project in smallest possible time. A wise man would choose fastapi for simplest syntax, less boilerplate circus and auto docs are of extreme importance when you debug you might not have do a hudred curls etc. You can always use express if you fancy that or maybe flask. But, I’ll strongly suggest sticking to fastapi

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def home():
    return "hello"

@app.get("/users/{user_id}")
def get_user(user_id):
    return {"user_id": user_id}

Now to run the simple server above.

# uvicorn <file name without py>:<name of fastapi object>
uvicorn server:app