cheat-sheet.md

C# quick start for Pythonistas

python	c#	notes
print "hello world"	Console.WriteLine("hello world");
import json	using Newtonsoft.Json;
myname = 'Tyson'	string myName = "Tyson"; -or- var myName = "Tyson"; (implicit type)
def do_thing():   # do that thing	void doThing() {   //do that thing }	"void" is the return type for "returns nothing" - if the function returned a string, it would be string doThing()
# this is a comment	// this is a single-line comment
for i in range(0,10):   print i	for(int i=0; i<10; i++) {   Console.WriteLine(i.ToString()); }
for dog in dogs:   pet(dog)	foreach(Dog dog in dogs) {   Pet(dog) }
if test1:   #do thing elif test2:   #do thing2 else test3:   #do thing3	if(test1) {   //do thing } else if (test2) {   //do thing2 } else {   //do thing3 }
[dog for dog in dogs if dog.weight > 100]	dogs.Where(dog => dog.Weight > 100)
instance = MyCustomClass()	MyCustomClass instance = new MyCustomClass();	(var works too)

Big Differences:

Whitespace don't matta!

C# is basically whitespace agnostic - format your lines and indentation however you damn well please. Instead, you'll see more {} brackets to enclose blocks and ; to end statements.

Strong typing

C# is a statically typed language, whereas python is dynamically typed. This means a few things:

• types are checked at compile-time, rather than at run-time
• variables can be declared without being assigned a value
• variables cannot change type, so, whereas python will let you do this:
  myvar = 'a kitten'
myvar = 45
myvar = {'bip': 'bop'}
  C# (generally) will not.
• this also means you have explicitly convert objects from one type to another, often via casting or explicit methods (like .ToString())

Compiled

As a somewhat innacurate generalization, Python is an interpreted language whereas C# is a compiled language. (in reality it is more complicated than this and both languages are kind of both but ¯\_(ツ)_/¯ ) For our purposes we can just say that in order to run c#, you must always "Build" it into a .dll or .exe.

Collections

There are some differences between the way python + C# handle collections. Python lists look a lot like C# arrays, but behave like C# lists. C# arrays are fixed-size, so you can't initialize them as [] and then add items to them. For variable sized collections, you'll need C# Lists (System.Collections.Generic.List<T>) which introduces another new topic - "Generics". Both lists and arrays in C# must know their type, and will not accept objects of a different type. Some general remarks:

• List<T> is slower than an array but much more flexible - usually it will be fine for your purposes.
• list + array access look just like python: MyList[5] will retun the 6th element in the collection.
• Setting up a list can look a little funky if you're used to Python:
  List<string> namesOfStuff = new List<string>();
  initializes an empty list. You can also populate a list at initialization, like so:
  var namesOfStuff = new List<string>{"Rock", "Plant", "Sofa", "Cheeky Neon", "Fruit Water"}; (note the {} instead of ())

Object-Orientation

Python lets you be as Object-oriented as you want - but it is possible to write python code that avoids object-orientation almost entirely. C# is much more opinionated about object-orientation, and has a lot of language features/architecture organized around OO practices. Python is much more flexible and free - it does less implicit hiding and protecting of class members, it's much easier to alter the behavior of code from modules borrowed from elsewhere. C# can be quite strict about what you're allowed to do, and good C# involves a lot of "encapsulation" which can feel foreign if you're used to python.