模块

编写模块

# fibo.py

# Fibonacci numbers module

def fib(n):    # write Fibonacci series up to n

    a, b = 0, 1

    while a < n:

        print(a, end=' ')

        a, b = b, a+b

    print()

def fib2(n):   # return Fibonacci series up to n

    result = []

    a, b = 0, 1

    while a < n:

        result.append(a)

        a, b = b, a+b

    return result

改变解释器的工作目录

How to know/change current directory in Python shell?

>>> import os

>>> os.getcwd()

'...'

>>> os.chdir("...")

导入（import） fibo 模块

>>> import fibo

>>> fibo.fib(1000)

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987

>>> fibo.fib2(100)

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]

>>> from fibo import fib, fib2

>>> fib(500)

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

>>> from fibo import *

>>> fib(500)

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

>>> import fibo as fib

>>> fib.fib(500)

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

>>> from fibo import fib as fibonacci

>>> fibonacci(500)

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

• 模块中可包含可执行语句，这些可执行语句只有在模块初次导入时才执行。
• 模块可导入其他模块。使用 modname.itemname 调用其他模块的函数。
• 可以将其他模块中的函数导入到本模块中。
• 使用通配符 * 时模块名不导入，以下划线打头的名字不导入。
• 模块名与其中的名字在导入时均可改名。

重新导入模块

How do I unload (reload) a Python module?

>>> import foo

>>> import importlib

>>> importlib.reload(foo)

标准模块

>>> import fibo,sys

>>> dir(fibo)

['__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'fib', 'fib2']

>>> a = [1, 2, 3, 4, 5]

>>> dir()

['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'a', 'fibo', 'os', 'sys']

异常

>>> # 使用 try ... except 处理异常

>>> while True:

    try:

        x = int(input("Please enter a number: "))

        break

    except ValueError:

        print("Oops!  That was no valid number.  Try again...")

Please enter a number: a

Oops!  That was no valid number.  Try again...

Please enter a number: 3

>>> # 异常类的继承

>>> class B(Exception):

    pass

>>> class C(B):

    pass

>>> class D(C):

    pass

>>> for cls in [B, C, D]:

    try:

        raise cls()

    except D:

        print("D")

    except C:

        print("C")

    except B:

        print("B")

B

C

D

>>> # 异常类的附带信息

>>> try:

    raise Exception('spam', 'eggs')

except Exception as inst:

    print(type(inst))    # the exception instance

    print(inst.args)     # arguments stored in .args

    print(inst)          # __str__ allows args to be printed directly,

                         # but may be overridden in exception subclasses

    x, y = inst.args     # unpack args

    print('x =', x)

    print('y =', y)

<class 'Exception'>

('spam', 'eggs')

('spam', 'eggs')

x = spam

y = eggs

>>> # else 和 finally

>>> def divide(x, y):

    try:

        result = x / y

    except ZeroDivisionError:

        print("division by zero!")

    else:

        print("result is", result)

    finally:

        print("executing finally clause")

>>> divide(2, 1)

result is 2.0

executing finally clause

>>> divide(2, 0)

division by zero!

executing finally clause

>>> divide("2", "1")

executing finally clause

Traceback (most recent call last):

  File "<pyshell#24>", line 1, in <module>

    divide("2", "1")

  File "<pyshell#21>", line 3, in divide

    result = x / y

TypeError: unsupported operand type(s) for /: 'str' and 'str'