Author | Logan Chien

  1. Item 18: Class and dict attribute

    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

for point_type in (Point, GoodPoint):
    print('----', point_type)
    p = point_type(1, 2)
    try:
        p.z = 3
    except AttributeError as e …

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  2. 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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  3. 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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  4. 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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  5. 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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  6. 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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  7. 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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  8. 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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  9. 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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  10. 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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