Python 学习笔记

 

>>> x = y = z = 0  # Zero x, y and z

a, b = 0, 1

>>> tax = 12.5 / 100
>>> price = 100.50
>>> price * tax
12.5625
>>> price + _
113.0625

>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> range(5, 10)
[5, 6, 7, 8, 9]
>>> range(0, 10, 3)
[0, 3, 6, 9]
>>> range(-10, -100, -30)
[-10, -40, -70]

The execution of a function introduces a new symbol table used for the local variables of the function. More precisely, all variable assignments in a function store the value in the local symbol table; whereas variable references first look in the local symbol table, then in the local symbol tables of enclosing functions, then in the global symbol table, and finally in the table of built-in names. Thus, global variables cannot be directly assigned a value within a function (unless named in a global statement), although they may be referenced.

The actual parameters (arguments) to a function call are introduced in the local symbol table of the called function when it is called; thus, arguments are passed using call by value (where the value is always an object reference, not the value of the object). [1] When a function calls another function, a new local symbol table is created for that call.

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



 In fact, even functions without a returnstatement do return a value, albeit a rather boring one. This value is called None

result = []

result.append(a) equivalent to result = result + [a]


 in keyword. This tests whether or not a sequence contains a certain value.

if ok in ('y', 'ye', 'yes'):
            return True

def f(a, L=[]):
    L.append(a)
    return L

print f(1)
print f(2)
print f(3)

The default value is evaluated only once!!!!

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

If you don’t want the default to be shared between subsequent calls, you can write the function like this instead:

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

a is required argument, L is optional argument

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

for idx, val in enumerate(ints):

　　print idx, val