python函数参数传递（**params）

def print_params_1(params):
    print params

def print_params_2(*params):
    print params
    
def print_params_3(**params):
    print params

上述3个函数参数，分别传递单参数、tuple、dictionary。

---

print_params_1('123')
print_params_1(1.0)
print_params_1('123',1)

输出

123
1.0
Traceback (most recent call last):

  File "", line 16, in
    print_params_1('123',1)

TypeError: print_params_1() takes exactly 1 argument (2 given)

---

print_params_2(1, 2, 3)
print_params_2(1.0)
print_params_2('x')

输出

(1, 2, 3)
(1.0,)
('x',)

---

print_params_3(x=1, y=2, z=3)
print_params_3(x=1)
print_params_3(1,2,3)

输出

{'y': 2, 'x': 1, 'z': 3}
{'x': 1}
Traceback (most recent call last):

  File "", line 3, in
    print_params_3(1,2,3)

TypeError: print_params_3() takes exactly 0 arguments (3 given)