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## Example files for the title:  

# Python in a Nutshell, by Alex Martelli

[![Python in a Nutshell, by Alex Martelli](http://akamaicovers.oreilly.com/images/9780596001889/cat.gif)](https://www.safaribooksonline.com/library/view/title/0596001886//)

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If you think your use of code examples falls outside fair use or the permission given here, feel free to contact us at <permissions@oreilly.com>.

Please note that the examples are not production code and have not been carefully testing. They are provided "as-is" and come with no warranty of any kind.

letter = 'c'

print "give me a", letter, "..."           # prints: give me a c ...

answer = 42

print "the answer is:", answer             # prints: the answer is: 42

----------

if x < 0: print "x is negative"

elif x % 2: print "x is positive and odd"

else: print "x is even and non-negative"

----------

if x < 0:

    print "x is negative"

elif x % 2:

    print "x is positive and odd"

else:

    print "x is even and non-negative"

----------

count = 0

while x > 0:

    x = x // 2            # truncating division

    count += 1

print "The approximate log2 is", count

----------

for letter in "ciao":

    print "give me a", letter, "..."

----------

for key, value in d.items():

    if not key or not value: del d[key]    # keep only true keys and values

----------

for x in someseq:

    process(x)

print "Last item processed was", x

----------

result1 = [x+1 for x in some_sequence]

----------

result2 = []

for x in some_sequence:

    result2.append(x+1)

----------

result3 = [x+1 for x in some_sequence if x>23]

----------

result4 = []

for x in some_sequence:

    if x>23:

        result4.append(x+1)

----------

result5 = [x+y for x in alist for y in another]

----------

result6 = []

for x in alist:

    for y in another:

        result6.append(x+y)

----------

while True:                     # this loop can never terminate naturally

    x = get_next()

    y = preprocess(x)

    if not keep_looping(x, y): break

    process(x, y)

----------

for x in some_container:

    if not seems_ok(x): continue

    lowbound, highbound = bounds_to_test()

    if x<lowbound or x>=highbound: continue

    if final_check(x):

        do_processing(x)

----------

for x in some_container:

    if seems_ok(x):

        lowbound, highbound = bounds_to_test()

        if lowbound<=x<highbound:

            if final_check(x):

                do_processing(x)

----------

for x in some_container:

    if is_ok(x): break             # item x is satisfactory, terminate loop

else:

    print "Warning: no satisfactory item was found in container"

    x = None

----------

if condition1(x):

    process1(x)

elif x>23 or condition2(x) and x<5:

    pass                                # nothing to be done in this case

elif condition3(x):

    process3(x)

else:

    process_default(x)

----------

inverse = {sin:asin, cos:acos, tan:atan, log:exp}

for f in inverse.keys(): inverse[inverse[f]] = f

----------

def double(x):

    return x*2

----------

def f(x, y=[]):

    y.append(x)

    return y

print f(23)                # prints: [23]

prinf f(42)                # prints: [23,42]

----------

def f(x, y=None):

    if y is None: y = []

    y.append(x)

    return y

print f(23)                # prints: [23]

prinf f(42)                # prints: [42]

----------

def sum(*numbers):

    result = 0

    for number in numbers: result += number

    return result

print sum(23,42)           # prints: 65

----------

def adict(**kwds): return kwds

print adict(a=23, b=42)    # prints: {'a':23, 'b':42}

----------

def adict(**kwds):

    return kwds

----------

def sum(*numbers):

    '''Accept arbitrary numerical arguments and return their sum.

    The arguments are zero or more numbers.  The result is their sum.'''

    result = 0

    for number in numbers: result += number

    return result

----------

def counter():

    counter.count += 1

    return counter.count

counter.count = 0

----------

def f(x, y):

    x = 23

    y.append(42)

a = 77

b = [99]

f(a, b)

print a, b                # prints: 77 [99, 42]

----------

def divide(divisor, dividend): return dividend // divisor

print divide(12,94)                         # prints: 7

print divide(dividend=94, divisor=12)       # prints: 7

----------

def f(middle, begin='init', end='finis'): return begin+middle+end

print f('tini', end='')                     # prints: inittini

----------

def sum(*numbers):

    result = 0

    for number in numbers: result += number

    return result

print sum(*d.values())

----------

_count = 0

def counter():

    global _count

    _count += 1

    return _count

----------

def percent1(a, b, c):                # works with any version

    def pc(x, total=a+b+c): return (x*100.0) / total

    print "Percentages are ", pc(a), pc(b), pc(c)

----------

def percent2(a, b, c):                # needs 2.2 or "from future import"

    def pc(x): return (x*100.0) / (a+b+c)

    print "Percentages are", pc(a), pc(b), pc(c)

----------

def make_adder_1(augend):             # works with any version

    def add(addend, _augend=augend): return addend+_augend

    return add

----------

def make_adder_2(augend):             # needs 2.2 or "from future import"

    def add(addend): return addend+augend

    return add

----------

aList = [1,2,3,4,5,6,7,8,9]

low = 3

high = 7

filter(lambda x,l=low,h=high: h>x>l, aList)     # returns: [4, 5, 6]

----------

aList = [1,2,3,4,5,6,7,8,9]

low = 3

high = 7

def test(value, l=low, h=high):

    return h>value>l

filter(test, aList)                             # returns: [4, 5, 6]

----------

def updown(N):

    for x in xrange(1,N): yield x

    for x in xrange(N,0,-1): yield x

for i in updown(3): print i                   # prints: 1 2 3 2 1

----------

def frange(start, stop, step=1.0):

    while start < stop:

        yield start

        start += step

class C1:

    x = 23

print C1.x                               # prints: 23

----------

class C2: pass

C2.x = 23

print C2.x                               # prints: 23

----------

C1.y = 45

C1.__dict__['z'] = 67

print C1.x, C1.y, C1.z                   # prints: 23, 45, 67

----------

class C3:

    x = 23

    y = x + 22                         # must use just x, not C3.x

----------

class C4:

    x = 23

    def amethod(self):

        print C4.x                     # must use C4.x, not just x

----------

class C5:

    def hello(self):

        print "Hello"

----------

anInstance = C5()

----------

class C6:

    def __init__(self,n):

        self.x = n

----------

anotherInstance = C6(42)

----------

anInstance.hello()                         # prints: Hello

print anotherInstance.x                    # prints: 42

----------

class C7: pass

z = C7()

z.x = 23

print z.x                                   # prints: 23

----------

z.y = 45

z.__dict__['z'] = 67

print z.x, z.y, z.z                         # prints: 23, 45, 67

----------

class SpecialCase:

    def amethod(self): print "special"

class NormalCase:

    def amethod(self): print "normal"

def appropriateCase(isnormal=1):

    if isnormal: return NormalCase()

    else: return SpecialCase()

aninstance = appropriateCase(isnormal=0)

aninstance.amethod()                        # prints "special", as desired

----------

class B:

    a = 23

    b = 45

    def f(self): print "method f in class B"

    def g(self): print "method g in class B"

class C(B):

    b = 67

    c = 89

    d = 123

    def g(self): print "method g in class C"

    def h(self): print "method h in class C"

x = C()

x.d = 77

x.e = 88

----------

def make_adder_as_closure(augend):

    def add(addend, _augend=augend): return addend+_augend

    return add

----------

def make_adder_as_bound_method(augend):

    class Adder:

        def __init__(self, augend): self.augend = augend

        def add(self, addend): return addend+self.augend

    return Adder(augend).add

----------

def make_adder_as_callable_instance(augend):

    class Adder:

        def __init__(self, augend): self.augend = augend

        def __call__(self, addend): return addend+self.augend

    return Adder(augend)

----------

class Base1:

    def amethod(self): print "Base1"

class Base2(Base1): pass

class Base3:

    def amethod(self): print "Base3"

class Derived(Base2, Base3): pass

aninstance = Derived()

aninstance.amethod()                    # prints: "Base1"

----------

class B:

    a = 23

    b = 45

    def f(self): print "method f in class B"

    def g(self): print "method g in class B"

class C(B):

    b = 67

    c = 89

    d = 123

    def g(self): print "method g in class C"

    def h(self): print "method h in class C"

----------

class Base:

    def greet(self, name): print "Welcome ", name

class Sub(Base):

    def greet(self, name):

        print "Well Met and",

        Base.greet(self, name)

x = Sub()

x.greet('Alex')

----------

class Base:

    def __init__(self):

        self.anattribute = 23

class Derived(Base):

    def __init__(self):

        Base.__init__(self)

        self.anotherattribute = 45

----------

class AClass(object):

    def astatic(): print 'a static method'

    astatic = staticmethod(astatic)

anInstance = AClass()

AClass.astatic()                    # prints: a static method

anInstance.astatic()                # prints: a static method

----------

class ABase(object):

    def aclassmet(cls): print 'a class method for', cls.__name__

    aclassmet = classmethod(aclassmet)

class ADeriv(ABase): pass

bInstance = ABase()

dInstance = ADeriv()

ABase.aclassmet()               # prints: a class method for ABase

bInstance.aclassmet()           # prints: a class method for ABase

ADeriv.aclassmet()              # prints: a class method for ADeriv

dInstance.aclassmet()           # prints: a class method for ADeriv

----------

class C(object):

    def __init__(self): pass

    # rest of class body omitted

----------

x = C.__new__(C, 23)

if isinstance(x, C): C.__init__(x, 23)

----------

class Singleton(object):

    _singletons = {}

    def __new__(cls, *args, **kwds):

        if not cls._singletons.has_key(cls):

            cls._singletons[cls] = object.__new__(cls)

        return cls._singletons[cls]

----------

class Rectangle(object):

    def __init__(self, width, heigth):

        self.width = width

        self.heigth = heigth

    def getArea(self):

        return self.width * self.heigth

    area = property(getArea, doc='area of the rectangle')

----------

attrib = property(fget=None, fset=None, fdel=None, doc=None)

----------

class Rectangle:

    def __init__(self, width, heigth):

        self.width = width

        self.heigth = heigth

    def getArea(self):

        return self.width * self.heigth

    def __getattr__(self, name):

        if name=  ='area': return self.getArea()

        raise AttributeError, name

    def __setattr__(self, name, value):

        if name=  ='area':

            raise AttributeError, "can't bind attribute"

        self.__dict__[name] = value

----------

class OptimizedRectangle(Rectangle):

    __slots__ = 'width', 'heigth'

----------

class listNoAppend(list):

    def __getattribute__(self, name):

        if name =  = 'append': raise AttributeError, name

        return list.__getattribute__(self, name)

----------

class AttributeWatcher:

    def __init__(self):

        # note the caution to avoid triggering __setattr__, and the

        # emulation of Python's name-mangling for a private attribute

        self.__dict__['_AttributeWatcher__mydict']={}

    def __getattr__(self, name):

        # as well as tracing every call, for demonstration purposes we

        # also fake "having" any requested attribute, EXCEPT special

        # methods (__getattr__ is also invoked to ask for them: check by

        # trying a few operations on an AttributeWatcher instance).

        print "getattr", name

        try: return self.__mydict[name]

        except KeyError:

            if name.startswith('__') and name.endswith('__'):

                raise AttributeError, name

            else: return 'fake_'+name

    def __setattr__(self, name, value):

        print "setattr", name, value

        self.__mydict[name] = value

    def __delattr__(self, name):

        print "delattr", name

        try: del self.__mydict[name]

        except KeyError: pass

----------

def fakeGetItem(idx): return idx

class Classic: pass

c = Classic()

c.__getitem__ = fakeGetItem

print c[23]                       # prints: 23

class NewStyle(object): pass

n = NewStyle()

n.__getitem__ = fakeGetItem

print n[23]                       # results in: 

# Traceback (most recent call last):

#   File "<stdin>", line 1, in ?

# TypeError: unindexable object

----------

class A(object):

    def met(self): 

        print 'A.met'

class B(A):

    def met(self): 

        print 'B.met'

        A.met(self)

class C(A):

    def met(self): 

        print 'C.met'

        A.met(self)

class D(B,C):

    def met(self): 

        print 'D.met'

        B.met(self)

        C.met(self)

----------

class A(object):

    def met(self): 

        print 'A.met'

class B(A):

    def met(self): 

        print 'B.met'

        super(B,self).met()

class C(A):

    def met(self): 

        print 'C.met'

        super(C,self).met()

class D(B,C):

    def met(self): 

        print 'D.met'

        super(D,self).met()

----------

class C:

    def __getslice__(self, i, j): print 'getslice', i, j

    def __getitem__(self, index): print 'getitem', index

x = C()

x[12:34]

x[56:78:9]

----------

for z in x:

    if y=  =z: return True

return False

----------

class Classic: pass

class Newstyle(object): pass

print type(Classic)                  # prints: <type 'class'>

print type(Newstyle)                 # prints: <type 'type'>

----------

class MyMeta(type):

    def __str__(cls): return "Beautiful class '%s'"%cls.__name__

class MyClass:

    __metaclass__ = MyMeta

x = MyClass()

print type(x)

----------

class Bunch(object):

    def __init__(self, **fields): self.__dict__ = fields

p = Bunch(x=2.3, y=4.5)

print p                     # prints: <__main__.Bunch object at 0x00AE8B10>

----------

class Point(MetaBunch):

    """ A point has x and y coordinates, defaulting to 0.0, and a color,

        defaulting to 'gray' -- and nothing more, except what Python and

        the metaclass conspire to add, such as __init__ and __repr__

    """

    x = 0.0

    y = 0.0

    color = 'gray'

# example uses of class Point

q = Point()

print q                     # prints: Point()

p = Point(x=1.2, y=3.4)

print p                     # prints: Point(y=3.399999999, x=1.2)