Python 入门指南之深入 Python 流程控制

>>> x = int(input("Please enter an integer: "))Please enter an integer: 42>>> if x < 0:...      x = 0...      print('Negative changed to zero')... elif x == 0:...      print('Zero')... elif x == 1:...      print('Single')... else:...      print('More')...More

>>> # Measure some strings:... words = ['cat', 'window', 'defenestrate']>>> for w in words:...     print(w, len(w))...cat 3window 6defenestrate 12

>>> for w in words[:]:  # Loop over a slice copy of the entire list....     if len(w) > 6:...         words.insert(0, w)...>>> words['defenestrate', 'cat', 'window', 'defenestrate']

>>> for i in range(5):...     print(i)...01234

range(5, 10)   5 through 9
range(0, 10, 3)   0, 3, 6, 9
range(-10, -100, -30)  -10, -40, -70

>>> a = ['Mary', 'had', 'a', 'little', 'lamb']>>> for i in range(len(a)):...     print(i, a[i])...0 Mary1 had2 a3 little4 lamb

>>> print(range(10))range(0, 10)

>>> list(range(5))[0, 1, 2, 3, 4]

>>> for n in range(2, 10):...     for x in range(2, n):...         if n % x == 0:...             print(n, 'equals', x, '*', n//x)...             break...     else:...         # loop fell through without finding a factor...         print(n, 'is a prime number')...2 is a prime number3 is a prime number4 equals 2 * 25 is a prime number6 equals 2 * 37 is a prime number8 equals 2 * 49 equals 3 * 3

>>> for num in range(2, 10):...     if num % 2 == 0:...         print("Found an even number", num)...         continue...     print("Found a number", num)Found an even number 2Found a number 3Found an even number 4Found a number 5Found an even number 6Found a number 7Found an even number 8Found a number 9

>>> while True:...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)...

>>> class MyEmptyClass:...     pass...

>>> def initlog(*args):...     pass   # Remember to implement this!...

>>> def fib(n):    # write Fibonacci series up to n...     """Print a Fibonacci series up to n."""...     a, b = 0, 1...     while a < n:...         print(a, end=' ')...         a, b = b, a+b...     print()...>>> # Now call the function we just defined:... fib(2000)0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597

>>> fib<function fib at 10042ed0>>>> f = fib>>> f(100)0 1 1 2 3 5 8 13 21 34 55 89

>>> fib(0)>>> print(fib(0))None

>>> def fib2(n): # return Fibonacci series up to n...     """Return a list containing the Fibonacci series up to n."""...     result = []...     a, b = 0, 1...     while a < n:...         result.append(a)    # see below...         a, b = b, a+b...     return result...>>> f100 = fib2(100)    # call it>>> f100                # write the result[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

def ask_ok(prompt, retries=4, complaint='Yes or no, please!'):    while True:        ok = input(prompt)        if ok in ('y', 'ye', 'yes'):            return True        if ok in ('n', 'no', 'nop', 'nope'):            return False        retries = retries - 1        if retries < 0:            raise OSError('uncooperative user')        print(complaint)

i = 5
def f(arg=i):    print(arg)
i = 6f()

def f(a, L=[]):    L.append(a)    return L
print(f(1))print(f(2))print(f(3))

[1][1, 2][1, 2, 3]

def f(a, L=None):    if L is None:        L = []    L.append(a)    return L

def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):    print("-- This parrot wouldn't", action, end=' ')    print("if you put", voltage, "volts through it.")    print("-- Lovely plumage, the", type)    print("-- It's", state, "!")

parrot(1000)                                          # 1 positional argumentparrot(voltage=1000)                                  # 1 keyword argumentparrot(voltage=1000000, action='VOOOOOM')             # 2 keyword argumentsparrot(action='VOOOOOM', voltage=1000000)             # 2 keyword argumentsparrot('a million', 'bereft of life', 'jump')         # 3 positional argumentsparrot('a thousand', state='pushing up the daisies')  # 1 positional, 1 keyword

parrot()                     # required argument missingparrot(voltage=5.0, 'dead')  # non-keyword argument after a keyword argumentparrot(110, voltage=220)     # duplicate value for the same argumentparrot(actor='John Cleese')  # unknown keyword argument

>>> def function(a):...     pass...>>> function(0, a=0)Traceback (most recent call last):  File "<stdin>", line 1, in ?TypeError: function() got multiple values for keyword argument 'a'

def cheeseshop(kind, *arguments, **keywords):    print("-- Do you have any", kind, "?")    print("-- I'm sorry, we're all out of", kind)    for arg in arguments:        print(arg)    print("-" * 40)    keys = sorted(keywords.keys())    for kw in keys:        print(kw, ":", keywords[kw])

cheeseshop("Limburger", "It's very runny, sir.",           "It's really very, VERY runny, sir.",           shopkeeper="Michael Palin",           client="John Cleese",           sketch="Cheese Shop Sketch")

-- Do you have any Limburger ?-- I'm sorry, we're all out of LimburgerIt's very runny, sir.It's really very, VERY runny, sir.----------------------------------------client : John Cleeseshopkeeper : Michael Palinsketch : Cheese Shop Sketch

def write_multiple_items(file, separator, *args):    file.write(separator.join(args))

>>> def concat(*args, sep="/"):...    return sep.join(args)...>>> concat("earth", "mars", "venus")'earth/mars/venus'>>> concat("earth", "mars", "venus", sep=".")'earth.mars.venus'

>>> list(range(3, 6))            # normal call with separate arguments[3, 4, 5]>>> args = [3, 6]>>> list(range(*args))            # call with arguments unpacked from a list[3, 4, 5]

>>> def parrot(voltage, state='a stiff', action='voom'):...     print("-- This parrot wouldn't", action, end=' ')...     print("if you put", voltage, "volts through it.", end=' ')...     print("E's", state, "!")...>>> d = {"voltage": "four million", "state": "bleedin' demised", "action": "VOOM"}>>> parrot(**d)-- This parrot wouldn't VOOM if you put four million volts through it. E's bleedin' demised !

>>> def make_incrementor(n):...     return lambda x: x + n...>>> f = make_incrementor(42)>>> f(0)42>>> f(1)43

>>> pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]>>> pairs.sort(key=lambda pair: pair[1])>>> pairs[(4, 'four'), (1, 'one'), (3, 'three'), (2, 'two')]

>>> def my_function():...     """Do nothing, but document it.......     No, really, it doesn't do anything....     """...     pass...>>> print(my_function.__doc__)Do nothing, but document it.
    No, really, it doesn't do anything.

>>> def f(ham: 42, eggs: int = 'spam') -> "Nothing to see here":...     print("Annotations:", f.__annotations__)...     print("Arguments:", ham, eggs)...>>> f('wonderful')Annotations: {'eggs': <class 'int'>, 'return': 'Nothing to see here', 'ham': 42}Arguments: wonderful spam