Python Basics

最近在复习Python，顺便记录一下自己的复习笔记，以后可以再回来看看。

Hello World

hello-world.py

if __name__ == "__main__":
    print "Hello, World."

分支

branch.py

if x==y:
    do_x_equal_y_stuff()
elif x==z:
    do_x_equal_z_stuff()
else:
    do_other_stuff()

循环

for-loop.py

for i in range(5):
    print i
    if i == j:
        break
    if i == k:
        continue
else:
    # do something if the loop end normally
    do_some_stuff()

while-loop.py

while x>0:
    x--
    print x
    if x == j:
        break
    if x == k:
        continue
else:
    #do something if the loop end normally
    do_some_stuff()

函数

simple-function.py

def add(a,b):
    ''' return the result of a plus b''' # docstring, need to be at the first line of the function
    return a+b

#call the function
print add(1,3)

local-global.py

x=10        # Here, x is global
def foo():
    x = 50  # Here, x is local, does not affect the global x
def bar():
    global x
    x= 8    # Here, x is global
# test
foo()
print x
bar()
print x

default-parameters.py

def add(a, b, c=0, d=3):
    return a+b+c+d

#call the function
print add(1, 3)
print add(1, 3, 4)
print add(1, 3, d=2)

list-and-dict-parameters.py

def foo(a, *l, **d):
    print a
    for list_item in l:
        print list_item
    for key,value in d:
        print "{k}:{v}".format(k=key, v=value)

# test
foo(1, ["x","y"], {"key": "value"})

类

__metaclass__ = type # new-style class
class ClassName(Parent1, Parent2):
    classVar = 0
    def __init__(self, parameter):
        super(ClassName, self).__init__(parameter)
        self.__class__.classVar += 1
        self.objectVar = 0
        pass
    def method(self, parameter):
        pass
    @classmethod
    def classMethod(cls, parameter):
        pass
    @staticmethod
    def staticMethod(parameter):
        pass

迭代器

__metaclass__ = type
class Fib:
    def __init__(self):
        self.first = 1
        self.second = 1
    def __iter__(self):
        return self   # a iterator returns a object which implements the 'next' method
    def next(self):   # if there is no next item, raise 'StopIteration' exception
        ret = self.first
        tmp = self.second
        self.second = self.second + self.first
        self.first = tmp
        return ret

生成器

def generator(l):
    for item in l:
        yield item

异常

import exceptions #standard exceptions

def foo(parameters):
    try:
        # do something
        if someCondition :
            raise SomeError
        if someOtherCondition:
            raise someErrorObject
        # do something
    except SomeError:
        raise    # raise the exception again
    except (SomeError1, SomeError2): # catch two types of exceptions at the same site
        # do something
    except (SomeError3), errorObject:
        # do something with errorObject
    except:
        # catch all exceptions
    else:
        # do something if no exception is raised
    finally:
        # do something whether there is any exception or not