Python revision

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Python data structures and classes

Python is an interpreted language
Python is completely object oriented
unlike C++ and Java, which have long, short for int, Python chooses the internal representation based on magnitude of its value.
Binary number start as 0b100101, Octal as 0o342, Hexadecimal as 0x7f
If string is passed to the int() constructor, it should be a number e.g (“123”), by default it should be decimal, to specify binary,octal,hexadecimal, pass it as (‘7f’,16)
Float class is the only floating-point type in Python. It uses fixed-point representation
Strings can be passed to the float constructor, if they are floating point or floating point literals. i.e float(“3.14”) and float(“2.0e3”) will be succesfully parsed and converted to floating point numbers
float doesn’t take binary, Octal or hexadecimal inputs
str class used for representing immutable, iterable strings
use \ for escape characters like “,’

list() construtor accepts any parameter of iterable type.
l = [1,2,3,4], k = l means k and l both point to the same list, and k[2] will change l[2]
Similar to arrays, but lists are dynamic. Implemented as circular linked lists, hence elements from the end can be accessed with a -, for example l[-1] will give last element, l[-2] will produce second last element
collections.dequeue() often useful is only first and last elements are useful

set is implemented using hash map in python
set only accepts items of immutable type
since lists are not immutable, one cannot have a set of lists or set of sets, but rather a set of tuples
for immutable sets use frozensets

Can return multiple items
Functions argument passing is neither call-by-reference, nor call-by-value. They are call-by-object reference
Python objects are not copied, this is oftne useful. Because of the call-by-object-reference model, mutable and immutable class of primitive data structures are very important to know. Passing mutable data types to functions should be done carefully.
functions can contain keyword arguments: def sum(a=0,b=0):. Here a and b are keyword arguments.

except DivdeByZeroError: print(“") ```

Lists are mutable, tuples are immutable
Python function are first-class objects, which allows them to be assigned to variables and be passed to functions
PEP-8 is a popular style guide to writing python code
Python has an array datatype as well, needs to be import, can hold elements of same datatype only unlike lists
lambda functions are annonymous functions
An iterable is an object that has an iter method which returns an iterator, or which defines a getitem method that can take sequential indexes starting from zero (and raises an IndexError when the indexes are no longer valid). So an iterable is an object that you can get an iterator from. An iterator is an object with a next method.
Packing and upacking using *args and **kwargs is a very elegant way to processing in Python. *args unpacks into a tuple, and **kwargs unpacks into a dictionary. It is not neccessary to use those names.
help() is a default method used to print docstring, dir() is a default method that returns all the attributes for an object, very useful for debugging
Also useful for debugging is logging module and debugger
map() function is used to iterate over a list and perform operation on it
python debugger is pdb
Generators are simple functions which return an iterable set of items, one at a time
In Python a variable is not an alias for a location in memory. Rather, it is simply a binding to a Python object