1. Item 17: Slots and Tracemalloc

    import tracemalloc
    
    class Point(object):
        def __init__(self, x, y):
            self.x = x
            self.y = y
    class GoodPoint(object):
        __slots__ = ('x', 'y')
        def __init__(self, x, y):
            self.x = x
            self.y = y
    
    def measure_heap(point_type):
        snapshot1 = tracemalloc.take_snapshot()
        x = [point_type(i, i) for i in range(1000000)]
        snapshot2 = tracemalloc …

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  2. Item 16: Iterate Generator

    def iterate_range(start, end):
        while start < end:
            yield start
            start += 1
    try:
        i = iterate_range(3, 5)
        print(repr(i))
        print(repr(iter(i)))
    
        while True:
            print(next(i))
    except StopIteration as e:
        print('Caught:', repr(e))
    

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  3. Item 15: Enumerable and iter function

    class RangeIterator(object):
        def __init__(self, start, end):
            self.i = start
            self.end = end
        def __next__(self):
            if self.i >= self.end:
                raise StopIteration(self.i)
            i = self.i
            self.i += 1
            return i
    class Range(object):
        def __init__(self, start, end):
            self.start = start
            self.end = end
        def __iter__ …

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  4. Item 14: Iterator and next Function

    class RangeIterator(object):
        def __init__(self, start, stop):
            self.i = start
            self.stop = stop
        def __next__(self):
            if self.i >= self.stop:
                raise StopIteration(self.i)
            i = self.i
            self.i += 1
            return i
    i = RangeIterator(3, 5)
    try:
        print(next(i, -1))
        print(next(i, -1))
        print(next(i …

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  5. Item 13: contextlib.closing()

    from contextlib import closing
    from http.client import HTTPSConnection
    from urllib.request import urlopen
    import re
    
    patt = re.compile('<h1>[^<]+</h1>')
    
    with urlopen('https://example.com') as f:
        content = f.read().decode('utf-8')
        print(patt.findall(content))
    
    with closing(HTTPSConnection('example.com')) as conn:
        conn.request('GET', '/')
        content = conn.getresponse …

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  6. Item 12: Nested with Statement

    class Resource(object):
        def __init__(self, id):
            assert id in (0, 1, 3, 4), "Bad ID"
            self.id = id
        def __enter__(self):
            print('Acquire', self)
            return self
        def __exit__(self, exc_type, exc_value, traceback):
            print('Release', self)
        def __str__(self):
            return 'resource_' + str(self.id)
    
    for i in range(3):
        print …

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  7. Item 11: Context Manager

    from contextlib import contextmanager
    
    @contextmanager
    def access_resource(name):
        print('Acquiring resource:', name)
        res = []
        try:
            yield res
        finally:
            print('Releasing resource:', name, res)
    
    with access_resource('To-Do List') as xs:
        print('Add To-Do Items')
        xs.append('Item 1')
        xs.append('Item 2')
    
    with access_resource('Finished List') as xs:
        raise KeyError('Impossible')
    

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  8. Item 10: with Statement

    class Logger(object):
        def __init__(self, i):
            self.msgs = []
            self.id = i
        def __enter__(self):
            print('BEGIN', self.id)
            return self.msgs
        def __exit__(self, exc_type, exc_value, traceback):
            print('END', self.id, exc_type, exc_value, traceback)
            for msg in self.msgs:
                print('NOTE', self.id, msg)
            return exc_type is ZeroDivisionError
    
    for …

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  9. Item 9: Function Decorator

    from functools import wraps
    
    def trace(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            a = ', '.join((repr(x) for x in args))
            print(func.__name__ + '(' + a + ')')
            return func(*args, **kwargs)
        return wrapper
    
    def fac1(n):
        return 1 if n == 0 else n * fac1(n - 1)
    fac1 = trace(fac1)
    
    @trace
    def fac2 …

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  10. Item 8: Lexical Scope

    def f(x):
        if x <= 1:
            return x
        return f(x - 1) + f(x - 2)
    
    g = f
    
    def f(x):
        return x
    
    print(f(23))
    print(g(23))
    

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