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Python中的异常由 try-except [exceptionname] 块处理，例如：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | def some_function(): try: # Division by zero raises an exception 10 / 0 except ZeroDivisionError: print "Oops, invalid." else: # Exception didn't occur, we're good. pass finally: # This is executed after the code block is run # and all exceptions have been handled, even # if a new exception is raised while handling. print "We're done with that." >>> some_function() Oops, invalid. We're done with that. |
外部库可以使用 import [libname] 关键字来导入。同时，你还可以用 from [libname] import [funcname] 来导入所需要的函数。例如：
1 2 3 4 5 6 | import random from time import clock randomint = random.randint(1, 100) >>> print randomint 64 |
Python针对文件的处理有很多内建的函数库可以调用。例如，这里演示了如何序列化文件(使用pickle库将数据结构转换为字符串)：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | import pickle mylist = ["This", "is", 4, 13327] # Open the file C:\\binary.dat for writing. The letter r before the # filename string is used to prevent backslash escaping. myfile = open(r"C:\\binary.dat", "w") pickle.dump(mylist, myfile) myfile.close() myfile = open(r"C:\\text.txt", "w") myfile.write("This is a sample string") myfile.close() myfile = open(r"C:\\text.txt") >>> print myfile.read() 'This is a sample string' myfile.close() # Open the file for reading. myfile = open(r"C:\\binary.dat") loadedlist = pickle.load(myfile) myfile.close() >>> print loadedlist ['This', 'is', 4, 13327] |
数值判断可以链接使用，例如 1<a<3 能够判断变量 a 是否在1和3之间。
可以使用 del 删除变量或删除数组中的元素。
列表推导式(List Comprehension)提供了一个创建和操作列表的有力工具。列表推导式由一个表达式以及紧跟着这个表达式的for语句构成，for语句还可以跟0个或多个if或for语句，来看下面的例子：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | >>> lst1 = [1, 2, 3] >>> lst2 = [3, 4, 5] >>> print [x * y for x in lst1 for y in lst2] [3, 4, 5, 6, 8, 10, 9, 12, 15] >>> print [x for x in lst1 if 4 > x > 1] [2, 3] # Check if an item has a specific property. # "any" returns true if any item in the list is true. >>> any([i % 3 for i in [3, 3, 4, 4, 3]]) True # This is because 4 % 3 = 1, and 1 is true, so any() # returns True. # Check how many items have this property. >>> sum(1 for i in [3, 3, 4, 4, 3] if i == 4) 2 >>> del lst1[0] >>> print lst1 [2, 3] >>> del lst1 |
全局变量在函数之外声明，并且可以不需要任何特殊的声明即能读取，但如果你想要修改全局变量的值，就必须在函数开始之处用global关键字进行声明，否则Python会将此变量按照新的局部变量处理（请注意，如果不注意很容易被坑）。例如：
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number = 5
def myfunc():
# This will print 5.
print number
def anotherfunc():
# This raises an exception because the variable has not
# been bound before printing. Python knows that it an
# object will be bound to it later and creates a new, local
# object instead of accessing the global one.
print number
number = 3
def yetanotherfunc():
global number
# This will correctly change the global.
number = 3
本教程并未涵盖Python语言的全部内容(甚至连一小部分都称不上)。Python有非常多的库以及很多的功能特点需要学习，所以要想学好Python你必须在此教程之外通过其它方式，例如阅读Dive into Python。希望这个教程能给你一个很好的入门指导。
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