we can establish new bindings using the assignment statement, which contains a name to the left of = and a value to the right
Names are also bound via import statements.
We can use assignment statements to give new names to existing functions.（我们可以通过赋值语句去使一个已经存在的函数绑定到一个名称）
successive assignment statements can rebind a name to a new value. （连续的赋值语句可以将名称绑定到一个新值）
One can even bind built-in names to new values.
（甚至可以将内置名称绑定到一个新值）
After assigning max to 5, the name max is no longer bound to a function, and so attempting to call max(2, 3, 4) will cause an error.
（在绑定max到5后，max不再绑定到函数，因此尝试调用max函数会导致错误）
When executing an assignment statement, Python evaluates the expression to the right of = before changing the binding to the name on the left. Therefore, one can refer to a name in right-side expression, even if it is the name to be bound by the assignment statement.
（当执行赋值语句时，Python在将绑定更改为左侧的名称之前，会对=右侧的表达式求值。因此，可以引用右侧表达式中的名称，即使它是要由赋值语句绑定的名称。）
We can also assign multiple values to multiple names in a single statement, where names on the left of = and expressions on the right of = are separated by commas.
（我们也可以在一条语句中分配多个值给多个名称，在等号的左边和右边用逗号进行分割）
>>> area, circumference = pi * radius * radius, 2 * pi * radius
Changing the value of one name does not affect other names
（更改一个名称的值不会影响到其他名称）
>>> area = pi * radius * radius
With multiple assignment, all expressions to the right of = are evaluated before any names to the left are bound to those values.
（对于多重赋值，在左侧的任何名称绑定到这些值之前将会对等式右边的所有表达式进行求值）
As a result of this rule, swapping the values bound to two names can be performed in a single statement.
（通过这个规则，在一个语句中交换两个名称的值是可以执行的）
