Python 101

Transcript

1. PYTHON 101
2. What is Python? ▪ Interpreted Language – don't have to compile it ▪ Multi-paradigm: OOP (no access specifiers), Functional and others... ▪ Guido van Rossum ("Benevolent Dictator For Life") ▪ Dynamic typing – Don't have to specify data types for variables ▪ Pythonic code and Zen of Python ▪ Cython, PyPy ▪ Indentation ▪ Built in garbage collector
3. Built in types ▪ Immutable built-in types of Python – Numbers – Strings – Tuples ▪ Mutable built-in types of Python – List – Dictionaries – Sets
4. Built in functions ▪ range([start], stop[, step]) ▪ sorted ▪ reversed ▪ And many more...
5. Examine ▪ type() ▪ dir() ▪ id() ▪ help()
6. Variables ▪ Local ▪ Global
7. Comments ▪ # ▪ ''' '''
8. Assignments = ▪ x = 2 ▪ C/C++: "typed variable name x receives a copy of numeric value 2". The (right-hand) value is copied into an allocated storage location for which the (left-hand) variable name is the symbolic address. ▪ Python: "(generic) name x receives a reference to a separate, dynamically allocated object of numeric (int) type of value 2."
9. Copies ▪ Deep – Nested Structures ▪ Shallow
10. Let's do some maths! ▪ // vs / ▪ ** ▪ Results of a division is always a float ▪ 1 is True 0 is False ▪ Is 2 True?
11. Comparisons ▪ == vs is (content vs type) ▪ and, or, not ▪ Can be chained
12. Strings ▪ "{} is {}".format("Sun", "hot") ▪ Can't change a string ▪ Try to avoid +
13. If else ▪ x if c else y ▪ elif ▪ Pass ▪ No switches
14. while while(condition): ...
15. Lists ▪ append, pop, remove, insert, index, extend ▪ Slicing ▪ :: ▪ list[start:end:step] ▪ join ▪ List comprehensions ▪ [:] deep copy ▪ in
16. for ▪ Calls iter() on object ▪ range – values on demand
17. def ▪ Functions are first class objects – I can assign them to variables ▪ Pass by value vs pass by reference ▪ *args – Variable number of args ▪ **kwargs – Variable number of keyword args
18. Maps and filters ▪ map(function, data) ▪ filter(function, data) ▪ Reduce
19. Try except ▪ Else – Runs only if no exceptions were raised ▪ Finally – Run everytime ▪ raise
20. Iterators and generators oh my! ▪ Iterable: Object with a __iter__ method which returns an iterator. You can put this in a for loop. ▪ Iterator: object with a __next__ method ▪ yield
21. classReverse: """Iterator for looping over a sequence backwards.""" def__init__(self, data): self.data = data self.index = len(data) def__iter__(self): returnself def__next__(self): if self.index == 0: raise StopIteration self.index = self.index - 1 returnself.data[self.index]
22. >>> rev = Reverse('spam') >>> iter(rev) <__main__.Reverse object at 0x00A1DB50> >>> for char in rev: ... print(char) ... m a p s
23. Generators ▪ All generators are iterators but not vice versa ▪ Produce values on demand ▪ Use yield instead of return ▪ Iter and next methods are created automatically
24. def reverse(data): for index in range(len(data)-1, -1, -1): yield data[index] >>>>>> for char in reverse('golf'): ... print(char) ... f l o g
25. Generator Expressions ▪ Lazy evaluation
26. Tuple ▪ Immutable ▪ Unpacking and swapping ▪ Initialization ▪ a, b = 1, 2
27. Dictionary ▪ What keys are hashable? ▪ get(), setdefault() ▪ Dict comprehensions ▪ {x: x+2 for x in range(1,100)}
28. Sets ▪ Elements of set have to be immutable ▪ & | - >= <= ▪ {x for x in range(1,100)}
29. class ▪ First class objects ▪ self ▪ isinstance
30. Feedback! ▪ http://bit.ly/2Awy91c