Python中流程控制语句的详细介绍

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

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

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

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

range(5, 10)   5 through 9range(0, 10, 3)   0, 3, 6, 9range(-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, reminder='Please try again!'):while True:
        ok = input(prompt)if ok in ('y', 'ye', 'yes'):return Trueif ok in ('n', 'no', 'nop', 'nope'):return Falseretries = retries - 1if retries < 0:raise ValueError('invalid user response')print(reminder)

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

i = 6f()

def f(a, L=[]):
    L.append(a)return Lprint(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 <module>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)for kw in keywords: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 Limburger
It's very runny, sir.It's really very, VERY runny, sir.----------------------------------------shopkeeper : Michael Palin
client : John Cleese
sketch : 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: str, eggs: str = 'eggs') -> str:
...     print("Annotations:", f.__annotations__)
...     print("Arguments:", ham, eggs)
...     return ham + ' and ' + eggs
...>>> f('spam')
Annotations: {'ham': <class 'str'>, 'return': <class 'str'>, 'eggs': <class 'str'>}
Arguments: spam eggs'spam and eggs'