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This is a simple knowledge point, but some students do not understand
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unpacking解包
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Solution, corresponding to * or **, there is also a saying of automatic unpacking
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iterable object corresponding to the package
Table of contents
1. Automatic unpacking
Assigned demo
a,b = [1,2]
print(a) # 1
print(b) # 2
Take out the elements in the container one by one and assign them separately
. It doesn’t have to be a list, it can be any iterable object such as a tuple, a dictionary, a string, etc.
For example, this
t1,t2 = (1,2)
s1,s2 = 'ab'
d1,d2 = {
'name':'wuxianfeng','age':18} # d1 是 name， d2 是age
However, it should be noted that the unpacking of the dictionary is just a key
.
a, *b, c = range(5) # b 就是[1,2,3]
2. Unpacking too much data*
Sometimes the data may be too much, then use the asterisk
a,b,c = 1,2,3,4
# 报错了
ValueError Traceback (most recent call last)
<ipython-input-6-e6e12dfe99e4> in <module>
----> 1 a,b,c = 1,2,3,4
ValueError: too many values to unpack (expected 3)
what to do?
a,*b,c = 1,2,3,4
# 此时的b的值为 [2, 3]，是个列表
# 如果这样
a,b,*c = 1,2,3,4 # 那么c就是[3,4]
sort of like this
list1 = [1,2,3,4,5,6,7,8]
first , rest = list1[0],list1[1:]
first , *rest = list1 # 以上两种写法一样的，都能让rest是 [2,3,4,5,6,7,8]
3. The use of asterisks in functions
code demo
def fun(x,y):
print(f'x={
x}')
print(f'y={
y}')
fun(1,2)
# 输出如下..
# x=1
# y=2
What if this is the case?
fun([1,2])
# 报错了
TypeError Traceback (most recent call last)
<ipython-input-8-6924a6444e6f> in <module>
----> 1 fun([1,2])
TypeError: fun() missing 1 required positional argument: 'y'
but it can
fun(*[1,2]) # x=1 y=2
fun(*'ab') # x=a y=b
fun(*(3,4)) # x=3 y=4
What if this is the case?
fun(*{
'name':'wuxianfeng','age':18})
# x=name
# y=age
What if this is the case?
for a, *b in [(1, 2, 3), (4, 5, 6, 7)]:
print(b)
Are the following two sentences correct? If yes, what is the value of a
*a, = range(5)
*a = range(5)
4. Unpacking of two asterisks
change function
def fun(x=1,y=2):
print(f'x={
x}')
print(f'y={
y}')
All previous tests were ok
If it is a dictionary, you have to pass the value into it
def fun(x=1,y=2):
print(f'x={
x}')
print(f'y={
y}')
fun(**{
'x':'wuxianfeng','y':18})
# 等价于
fun(x='wuxianfeng',y=18)
Specifically, you can look at the definition and application of the indeterminate parameters of the function, and I will not explain more here
Five, the application of the scene
merge dictionaries
d1 = {
'x':1}
d2 = {
'y':2}
d3 = {
**d1,**d2}
d3 # {'x': 1, 'y': 2}
The same list can also be merged
li1 = [1,2]
li2 = [3,4]
li3 = [*li1,*li2]
li3
zip is an interesting built-in function
like this
li1 = ['a','b']
li2 = [1,2]
li = list(zip(li1,li2))
li # [('a', 1), ('b', 2)]
di = dict(zip(li1,li2)) # {'a': 1, 'b': 2}
# 如果要逆向呢？
li1 = ['a','b']
li2 = [1,2]
result = zip(li1,li2)
print(list(zip(*result))) # [('a', 'b'), (1, 2)]
Back to the topic, in the selenium course, there is such a paragraph
def find_element(self, by=By.ID, value=None) -> WebElement:
pass
# 在后面项目课中的调用我们是这样做的
locator = 'id','ls_username'
driver.find_element(*locator)
# 如果这样driver.find_element(locator) 显然报错在上面已经提到了。
