Detail python unpacking iterative data such as tuple list

Unpacking is the splitting of data in a structure into separate variables.

Take tuples as an example:

>>> a = ('windows', 10, 25.1, (2017, 12, 29))

Suppose the data means buying 10 copies of windows, each worth $25.1. The data was acquired on December 29, 2017.

We need to get the price per copy of this data:

>>> a[2]

Unpacking can also be used:

>>>os_type, number, price, dat = a
>>>price

Note that unpacking objects must be iteratable such as tuple and list.

Question 2: We only care about price and date, not system and quantity:

Use an unused variable and then match the first two terms with the adaptation symbol *.

>>> *_, price, dat = a
>>> price
>>>dat

Third, if we only care about the price and the month, how do we unlock the bag?

>>> *_, price, (_, m, d) = a
>>> price
>>> m

Note that unpacking is supported in python, but started in python3 with * to match multiple values. So pay attention to the python version information when using *.

Question: If the left and right Numbers do not match and * is not used, what will the result be?

ValueError: too many values to unpack

>>> _, price, (*_, m, d) =a
Traceback (most recent call last):
 File "<pyshell#10>", line 1, in <module>
 _, price, (*_, m, d) =a
ValueError: too many values to unpack (expected 3)

conclusion