Python 教程 17 — 类和方法

"""This module contains a code example related to
Think Python, 2nd Edition
by Allen Downey
http://thinkpython2.com
Copyright 2015 Allen Downey
License: http://creativecommons.org/licenses/by/4.0/
"""

from __future__ import print_function, division


class Time:
    """Represents the time of day.
       
    attributes: hour, minute, second
    """
    def __init__(self, hour=0, minute=0, second=0):
        """Initializes a time object.
        hour: int
        minute: int
        second: int or float
        """
        self.hour = hour
        self.minute = minute
        self.second = second

    def __str__(self):
        """Returns a string representation of the time."""
        return '%.2d:%.2d:%.2d' % (self.hour, self.minute, self.second)

    def print_time(self):
        """Prints a string representation of the time."""
        print(str(self))

    def time_to_int(self):
        """Computes the number of seconds since midnight."""
        minutes = self.hour * 60 + self.minute
        seconds = minutes * 60 + self.second
        return seconds

    def is_after(self, other):
        """Returns True if t1 is after t2; false otherwise."""
        return self.time_to_int() > other.time_to_int()

    def __add__(self, other):
        """Adds two Time objects or a Time object and a number.
        other: Time object or number of seconds
        """
        if isinstance(other, Time):
            return self.add_time(other)
        else:
            return self.increment(other)

    def __radd__(self, other):
        """Adds two Time objects or a Time object and a number."""
        return self.__add__(other)

    def add_time(self, other):
        """Adds two time objects."""
        assert self.is_valid() and other.is_valid()
        seconds = self.time_to_int() + other.time_to_int()
        return int_to_time(seconds)

    def increment(self, seconds):
        """Returns a new Time that is the sum of this time and seconds."""
        seconds += self.time_to_int()
        return int_to_time(seconds)

    def is_valid(self):
        """Checks whether a Time object satisfies the invariants."""
        if self.hour < 0 or self.minute < 0 or self.second < 0:
            return False
        if self.minute >= 60 or self.second >= 60:
            return False
        return True


def int_to_time(seconds):
    """Makes a new Time object.
    seconds: int seconds since midnight.
    """
    minutes, second = divmod(seconds, 60)
    hour, minute = divmod(minutes, 60)
    time = Time(hour, minute, second)
    return time


def main():
    start = Time(9, 45, 00)
    start.print_time()

    end = start.increment(1337)
    #end = start.increment(1337, 460)
    end.print_time()

    print('Is end after start?')
    print(end.is_after(start))

    print('Using __str__')
    print(start, end)

    start = Time(9, 45)
    duration = Time(1, 35)
    print(start + duration)
    print(start + 1337)
    print(1337 + start)

    print('Example of polymorphism')
    t1 = Time(7, 43)
    t2 = Time(7, 41)
    t3 = Time(7, 37)
    total = sum([t1, t2, t3])
    print(total)


if __name__ == '__main__':
    main()

from __future__ import print_function, division


class Point:
    """Represents a point in 2-D space.
    attributes: x, y
    """
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return '(%g, %g)' % (self.x, self.y)

class Point:
    """Represents a point in 2-D space.
    attributes: x, y
    """
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return '(%g, %g)' % (self.x, self.y)

def main():
    p1 = Point(1, 2)
    p2 = Point(3, 4)
    print(p1)
    print(p2)

from __future__ import print_function, division


class Point:
    """Represents a point in 2-D space.
    attributes: x, y
    """
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return '(%g, %g)' % (self.x, self.y)

    def __add__(self, other):
        """Adds a Point or tuple."""
        if isinstance(other, Point):
            return self.add_point(other)
        elif isinstance(other, tuple):
            return self.add_tuple(other)
        else:
            msg = "Point doesn't know how to add type " + type(other)
            raise TypeError(msg)

from __future__ import print_function, division


class Point:
    """Represents a point in 2-D space.
    attributes: x, y
    """
    def __init__(self, x=0, y=0):
        self.x = x
        self.y = y

    def __str__(self):
        return '(%g, %g)' % (self.x, self.y)

    def __add__(self, other):
        """Adds a Point or tuple."""
        if isinstance(other, Point):
            return self.add_point(other)
        elif isinstance(other, tuple):
            return self.add_tuple(other)
        else:
            msg = "Point doesn't know how to add type " + type(other)
            raise TypeError(msg)

    def add_point(self, other):
        """Adds a point."""
        return Point(self.x + other.x, self.y + other.y)

    def add_tuple(self, other):
        """Adds a tuple."""
        return Point(self.x + other[0], self.y + other[1])
def main():
    p1 = Point(1, 2)
    p2 = Point(3, 4)
    print(p1)
    print(p2)
    print(p1 + p2)
    print(p1 + (3, 4))

if __name__ == '__main__':
    main()

"""This module contains a code example related to
Think Python, 2nd Edition
by Allen Downey
http://thinkpython2.com
Copyright 2015 Allen Downey
License: http://creativecommons.org/licenses/by/4.0/
"""

from __future__ import print_function, division


class Time:
    """Represents the time of day.
       
    attributes: hour, minute, second
    """
    def __init__(self, hour=0, minute=0, second=0):
        """Initializes a time object.
        hour: int
        minute: int
        second: int or float
        """
        minutes = hour * 60 + minute
        self.seconds = minutes * 60 + second

    def __str__(self):
        """Returns a string representation of the time."""
        minutes, second = divmod(self.seconds, 60)
        hour, minute = divmod(minutes, 60)
        return '%.2d:%.2d:%.2d' % (hour, minute, second)

    def print_time(self):
        """Prints a string representation of the time."""
        print(str(self))

    def time_to_int(self):
        """Computes the number of seconds since midnight."""
        return self.seconds

    def is_after(self, other):
        """Returns True if t1 is after t2; false otherwise."""
        return self.seconds > other.seconds

    def __add__(self, other):
        """Adds two Time objects or a Time object and a number.
        other: Time object or number of seconds
        """
        if isinstance(other, Time):
            return self.add_time(other)
        else:
            return self.increment(other)

    def __radd__(self, other):
        """Adds two Time objects or a Time object and a number."""
        return self.__add__(other)

    def add_time(self, other):
        """Adds two time objects."""
        assert self.is_valid() and other.is_valid()
        seconds = self.seconds + other.seconds
        return int_to_time(seconds)

    def increment(self, seconds):
        """Returns a new Time that is the sum of this time and seconds."""
        seconds += self.seconds
        return int_to_time(seconds)

    def is_valid(self):
        """Checks whether a Time object satisfies the invariants."""
        return self.seconds >= 0 and self.seconds < 24*60*60


def int_to_time(seconds):
    """Makes a new Time object.
    seconds: int seconds since midnight.
    """
    return Time(0, 0, seconds)


def main():
    start = Time(9, 45, 00)
    start.print_time()

    end = start.increment(1337)
    end.print_time()

    print('Is end after start?')
    print(end.is_after(start))

    print('Using __str__')
    print(start, end)

    start = Time(9, 45)
    duration = Time(1, 35)
    print(start + duration)
    print(start + 1337)
    print(1337 + start)

    print('Example of polymorphism')
    t1 = Time(7, 43)
    t2 = Time(7, 41)
    t3 = Time(7, 37)
    total = sum([t1, t2, t3])
    print(total)


if __name__ == '__main__':
    main()

"""This module contains a code example related to
Think Python, 2nd Edition
by Allen Downey
http://thinkpython2.com
Copyright 2015 Allen Downey
License: http://creativecommons.org/licenses/by/4.0/
"""

from __future__ import print_function, division

"""
WARNING: this program contains a NASTY bug.  I put
it there on purpose as a debugging exercise, but
you DO NOT want to emulate this example!
"""

class Kangaroo:
    """A Kangaroo is a marsupial."""
    
    def __init__(self, name, contents=[]):
        """Initialize the pouch contents.
        name: string
        contents: initial pouch contents.
        """
        self.name = name
        self.pouch_contents = contents

    def __str__(self):
        """Return a string representaion of this Kangaroo.
        """
        t = [ self.name + ' has pouch contents:' ]
        for obj in self.pouch_contents:
            s = '    ' + object.__str__(obj)
            t.append(s)
        return '\n'.join(t)

    def put_in_pouch(self, item):
        """Adds a new item to the pouch contents.
        item: object to be added
        """
        self.pouch_contents.append(item)


kanga = Kangaroo('Kanga')
roo = Kangaroo('Roo')
kanga.put_in_pouch('wallet')
kanga.put_in_pouch('car keys')
kanga.put_in_pouch(roo)

print(kanga)

# If you run this program as is, it seems to work.
# To see the problem, trying printing roo.

# Hint: to find the problem try running pylint.

"""This module contains a code example related to
Think Python, 2nd Edition
by Allen Downey
http://thinkpython2.com
Copyright 2015 Allen Downey
License: http://creativecommons.org/licenses/by/4.0/
"""

from __future__ import print_function, division

"""
WARNING: this program contains a NASTY bug.  I put
it there on purpose as a debugging exercise, but
you DO NOT want to emulate this example!
"""

class Kangaroo:
    """A Kangaroo is a marsupial."""
    
    def __init__(self, name, contents=[]):
        """Initialize the pouch contents.
        name: string
        contents: initial pouch contents.
        """
        # The problem is the default value for contents.
        # Default values get evaluated ONCE, when the function
        # is defined; they don't get evaluated again when the
        # function is called.

        # In this case that means that when __init__ is defined,
        # [] gets evaluated and contents gets a reference to
        # an empty list.

        # After that, every Kangaroo that gets the default
        # value gets a reference to THE SAME list.  If any
        # Kangaroo modifies this shared list, they all see
        # the change.

        # The next version of __init__ shows an idiomatic way
        # to avoid this problem.
        self.name = name
        self.pouch_contents = contents

    def __init__(self, name, contents=None):
        """Initialize the pouch contents.
        name: string
        contents: initial pouch contents.
        """
        # In this version, the default value is None.  When
        # __init__ runs, it checks the value of contents and,
        # if necessary, creates a new empty list.  That way,
        # every Kangaroo that gets the default value gets a
        # reference to a different list.

        # As a general rule, you should avoid using a mutable
        # object as a default value, unless you really know
        # what you are doing.
        self.name = name
        if contents == None:
            contents = []
        self.pouch_contents = contents

    def __str__(self):
        """Return a string representaion of this Kangaroo.
        """
        t = [ self.name + ' has pouch contents:' ]
        for obj in self.pouch_contents:
            s = '    ' + object.__str__(obj)
            t.append(s)
        return '\n'.join(t)

    def put_in_pouch(self, item):
        """Adds a new item to the pouch contents.
        item: object to be added
        """
        self.pouch_contents.append(item)


kanga = Kangaroo('Kanga')
roo = Kangaroo('Roo')
kanga.put_in_pouch('wallet')
kanga.put_in_pouch('car keys')
kanga.put_in_pouch(roo)

print(kanga)
print(roo)

# If you run this program as is, it seems to work.
# To see the problem, trying printing roo.