Python

- functions are first class objects, that means they can be passed as args to other functions.
 type(funcName()): prints the return type of the function 
- help(funcs): prints the help output 
- Calling a function without () returns the reference to that func, but with () returns the returns. 
- Decorator: is a callable that takes another function as an argument and extending the behavior of that function without explicitly modifying that function.  
- Decorator can access and modify input arguments and the return values. 
- The super() function is used to give access to methods and properties of a parent or sibling class. The super() function returns an object that represents the parent class. 
- Magic methods: a set of methods that python automatically associates with each class. We can override this methods to customize the methods.  
- Any object is considered boolean true, unless it has a link or has some special values that make it false (None/Flase/Numeric zero values (0,0.0,0j/Decimal(0)/Fraction(0,x)/Empty sequences/collections: '', (),[],{}/empty sets and ranges: set(), range(0)). And also if you override the value of __bool__ to false, or __len__ to 0 in a class. 
- To check the boolean value of something in python: bool(x).
- walrus operator in python is the assignment expression that helps to write concise code. For example:

thestr = input("value? ")
while thestr != "exit":
    print(thestr)
    thestr = input("value? ")

TO

while (thestr := input("value? ")) != "exit":
    print(thestr)

Another example, to reduce function calls:
values = [12, 0, 10, 5, 9, 18, 41, 23, 30, 16, 18, 9, 18, 22]
val_data = {
    "length": (l := len(values)),
    "total": (s := sum(values)),
    "average": s / l
}

- you can change, separator and ending of print statement:
values=["one", "two", "three", "four", "five"]
print(*values)

# use the 'sep' argument to control the separator between values:
print(*values, sep=' -- ')

# use the 'end' argument to control the line ending characters
# let's auto-print the current line number along with each item
for i in range(0, len(values)):
    print(values[i], end=f" [line: {str(i+1)}]\n")

you can also use print to print in file:
newfile = open("output.txt","w")
print(*values, sep=' -- ', file=newfile, flush=True)
newfile.close()
- pretty print (link to help: https://docs.python.org/3/library/pprint.html)

--- iterators:
- i = iter(list), next(i)
- enumerate:
days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]
for i, m in enumerate(days, start=1):
    print(i, m)
- use zip to combine sequences, if the lists are not equal in size, it stops when the short list ends :
for m in zip(days, daysFr):
    print(m)

- zip_longest, fills the values of shorter list:

import itertools
# use zip_longest
seq1 = ["A","B","C","D","E","F"]
seq2 = [1, 2, 3, 4]
seq3 = "xyz"
result = itertools.zip_longest(seq1, seq2, seq3, fillvalue="-")
print("Result: ")
for item in result:
    print(item)
Result: 
('A', 1, 'x')
('B', 2, 'y')
('C', 3, 'z')
('D', 4, '-')
('E', '-', '-')
('F', '-', '-')

- function has lib called itertools: https://docs.python.org/3/library/itertools.html
# cycle iterator can be used to cycle over a collection infinitely -  as long as you call next, it iterates
names = ["Joe", "Jane", "Jim"]
cycler = itertools.cycle(names)
print(next(cycler))
print(next(cycler))
print(next(cycler))
print(next(cycler))

# use count to create a simple counter -  as long as you call next, it iterates
counter = itertools.count(100, 10)
print(next(counter))
print(next(counter))
print(next(counter))

##
vals = [10,20,30,40,50,40,30]
acc = itertools.accumulate(vals, max)
print(list(acc))

- chain
# chain() creates a single iterable from multiple
x = itertools.chain("ABCD", "1234")
print(list(x))

s1 = "ABCDEFG"
s2 = [1,2,3,4,5]
s3 = ['$','%','@','&']
result = itertools.chain.from_iterable([s1,s2,s3])
print(list(result))