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\ No newline at end of file +**/auto +**/.ipynb_checkpoints diff --git a/advanced_python/16_generators.ipyml b/advanced_python/16_generators.ipyml new file mode 100644 index 0000000..b30162d --- /dev/null +++ b/advanced_python/16_generators.ipyml @@ -0,0 +1,390 @@ +cells: + +- markdown: | + # Advanced Python: Iterators and Generators + + ### Prabhu Ramachandran + ### The FOSSEE Python group & + ### Department of Aerospace Engineering + ### IIT Bombay + + metadata: + slideshow: + slide_type: slide + + +- markdown: | + ## Background + + - Container objects present a similar interface + - They can all be looped over using `for` + + metadata: + slideshow: + slide_type: slide + +- code: | + for i in [1, 2, 3]: + print(i) + + for key in {'a': 1, 'b': 2}: + print(key) + + for char in 'hello world': + print(char) + + for line in open('file.txt'): + print(line, end='') + +- markdown: | + ## Background + + - Similar interface for different objects + - These objects are all **iterable** + - They are all **iterators** + + metadata: + slideshow: + slide_type: subslide + +- markdown: | + ## Introduction + + - This is a powerful feature/abstraction + - Easy to create your own iterators + <br/> + <br/> + + metadata: + slideshow: + slide_type: slide + +- markdown: | + - A **generator** makes it easy to create an iterator + - How would you write a `range` function? + <br/> + <br/> + + - Use the `yield` keyword + + metadata: + slideshow: + slide_type: fragment + +- code: | + def counter(n): + count = 0 + while count < n: + yield count + count += 1 + + metadata: + slideshow: + slide_type: slide + +- code: | + c = counter(2) + +- code: | + next(c) + +- code: | + next(c) + +- code: | + next(c) + +- code: | + for i in counter(4): + print(i) + + metadata: + slideshow: + slide_type: slide + +- markdown: | + ## Observations + + - Note that `yield` resumes the function + - The function/method remembers its state + - It can yield any object + - An empty `yield` is also acceptable + - You can have multiple yields + + metadata: + slideshow: + slide_type: slide + +- code: | + def infinite_generator(): + while True: + yield + + metadata: + slideshow: + slide_type: fragment + +- markdown: | + ## Exercise: simple generator + + Write a simple generator that generates the first `n` odd numbers. Call this + function `odd(n)`. + + metadata: + slideshow: + slide_type: slide + +- code: | + for x in odd(5): + print(x) + +- markdown: | + ## Solution + + metadata: + slideshow: + slide_type: slide + +- code: | + def odd(n): + for i in range(n): + yield 2*i + 1 + + +- markdown: | + ## Exercise: Fibonacci generator + + Write a simple generator that returns the first `n` numbers of the Fibonacci + sequence, call this function `fib(n)`. + + metadata: + slideshow: + slide_type: slide + +- code: | + for x in fib(5): + print(x) + +- markdown: | + ## Solution + + metadata: + slideshow: + slide_type: slide + +- code: | + def fib(n): + a, b = 0, 1 + yield 0 + for i in range(n-1) + yield b + a, b = b, a + b + + +# --------------- Part 2 -------------- + +- markdown: | + ## Creating iterable objects + + - What if you want to create an object that is iterable? + - Overload the `__iter__` and/or `__next__` methods. + - Recall our `Zoo` class? + + metadata: + slideshow: + slide_type: slide + +- code: | + class Zoo: + def __init__(self, *animals): + self.animals = list(animals) + +- markdown: | + We want the following to work, + + metadata: + slideshow: + slide_type: slide + +- code: | + c = Animal('crow') + m = Mammal('dog') + z = Zoo(c, m) + + for animal in z: + animal.greet() + +- markdown: | + ## Making `Zoo` iterable + + - Overload the `__iter__` to return an iterable + - An iterable should have a `__next__` method + + metadata: + slideshow: + slide_type: slide + +- code: | + class Zoo: + def __init__(self, *animals): + self.animals = list(animals) + + def __iter__(self): + return self.animals + +- code: | + c = Animal('crow') + m = Mammal('dog') + z = Zoo(c, m) + + for animal in z: + animal.greet() + + metadata: + slideshow: + slide_type: slide + +- markdown: | + ## Observations + + - Just returns `self.animals` + - `self.animals` is iterable as it is a list + + metadata: + slideshow: + slide_type: slide + +- markdown: | + ## A more complex example + + - What if we cannot just return an internal list? + - We must provide a `__next__` method + - To stop the iteration: `raise StopIteration` + + metadata: + slideshow: + slide_type: slide + +- code: | + class SimpleRange: + def __init__(self, n): + self.n = n + self.count = 0 + def __iter__(self): + return self + def __next__(self): + if self.count == self.n: + raise StopIteration + self.count += 1 + return self.count + + metadata: + slideshow: + slide_type: subslide + +- code: | + r = SillyRange(5) + for i in r: + print(i) + + metadata: + slideshow: + slide_type: subslide + + +- markdown: | + ## Observations + + - Useful when you want an object to be iterable + - Notice the `__next__` method + - Notice the `raise StopIteration` + - Easier to use functions/methods with `yield` + + metadata: + slideshow: + slide_type: slide + + +- markdown: | + ## Summary + + - Easy to use and write + - Allows one to abstract a loop + - `yield` for functions and methods + - Overload `__iter__, __next__` for objects + + metadata: + slideshow: + slide_type: slide + + +- markdown: | + ## Exercise: Fibonacci generator object + + Create a class that when instantiated with an argument `n` can be used as a + sequence of the first `n` numbers of the Fibonacci sequence, call this + class `Fib`. + + metadata: + slideshow: + slide_type: slide + +- code: | + f = Fib(5) + for x in f: + print(x) + +- markdown: | + ## Solution + + metadata: + slideshow: + slide_type: slide + +- code: | + class Fib: + def __init__(self, n): + self.count = n + self.a, self.b = 0, 1 + def __iter__(self): + return self + def __next__(self): + if self.count == 0: + raise StopIteration + old = self.a + self.count -= 1 + self.a, self.b = self.b, self.a + self.b + return old + +- code: | + f = Fib(5) + for i in f: + print(i) + + metadata: + slideshow: + slide_type: slide + + +# The lines below here may be deleted if you do not need them. +# --------------------------------------------------------------------------- +metadata: + kernelspec: + display_name: Python 3 + language: python + name: python3 + language_info: + codemirror_mode: + name: ipython + version: 3 + file_extension: .py + mimetype: text/x-python + name: python + nbconvert_exporter: python + pygments_lexer: ipython3 + version: 3.6.0 + rise: + scroll: true + transition: none +nbformat: 4 +nbformat_minor: 2 diff --git a/advanced_python/rise.css b/advanced_python/rise.css new file mode 100644 index 0000000..11d733d --- /dev/null +++ b/advanced_python/rise.css @@ -0,0 +1,21 @@ +/* Customizations for RISE slides + */ + +/* Increase font size for the code cells. +*/ + +div.cell.code_cell { + font-size: 150%; +} + +/* +div.CodeMirror-lines { + font-size: 125%; +}*/ + +/* Tables were rendered out as tiny values + since the font-size was set to 12px somehow. +*/ +.rendered_html table { + font-size: 100% +} |