python元组打包和解包过程详解

在将多个以逗号分隔的值赋给一个变量时，多个值被打包成一个元组类型。当我们将一个元组赋给多个变量时，它将解包成多个值，然后分别将其赋给相应的变量。

# 打包
a = 1, 10, 100
print(type(a), a)    # <class 'tuple'> (1, 10, 100)
# 解包
i, j, k = a
print(i, j, k)       # 1 10 100

解包时，如果解包出来的元素数目与变量数目不匹配，就会引发ValueError异常。错误信息为：too many values to unpack（解包的值太多）或not enough values to unpack（解包的值不足）。

a = 1, 10, 100, 1000
# i, j, k = a             # ValueError: too many values to unpack (expected 3)
# i, j, k, l, m, n = a    # ValueError: not enough values to unpack (expected 6, got 4)

知识点扩充：

python之打包，解包

#coding:utf-8
#字符串，列表，元组打包与解包
aString = 'abc'
aList = [1, 2, 3]
aTuple = 'a', 'A', 1

print('Unpacking string......')
first, second, third = aString
print("string values:", first, second, third)

print('\nUnpacking list......')
first, second, third = aList
print("string values:", first, second, third)

print('\nUnpacking tuple......')
first, second, third = aTuple
print("string values:", first, second, third)

#swapping two values
x = 3
y = 4
print('\nBefore swapping: x = %d,y =%d' % (x, y))
#首先将右边的部分打包成一个元组，即（4，3），而后解包指派给变量x,y
x, y = y, x #swap Variables
print('After swapping: x = %d, y = %d' % (x, y))

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