July 2017
Intermediate to advanced
398 pages
11h 54m
Chinese
Content preview from Python数据处理
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rec_key = item.attrib[lookup_key]
print
rec_key
修改完成后，在命令行中重新运行代码。对于每一条数据记录，我们得到下面的值：
PUBLISHSTATE
COUNTRY
WORLDBANKINCOMEGROUP
YEAR
SEX
GHO
REGION
49.00000
看起来都很适合做新字典的键，除了最后一个。这是因为最后一个元素是
Numeric
字典，
而不是我们要处理的
Category
字典。如果想保留这些数据供后续使用，需要用
if
语句为
这些数值元素创建一种特殊情况。
Python
的
if
语句
if
语句最基本的形式，是用来控制代码流的方法。
if
语句是在告诉代码：如果满足该
条件，那就执行给定的命令。
if
语句的另一种用法是与
else
一起使用。
if-else
语句的意思是：如果满足第一个条
件，那么执行相应的命令；但如果不满足该条件，那么执行
else
语句中的命令。
除了
if
和
if-else
之外，你还会将
==
作为比较运算符。
==
用来给变量赋值，而
==
用来检验两个值是否相等。另外，
!=
用来检验两个值是否不相等。这两个运算符返回
的都是布尔值：
True
或
False
。
在
Python
解释器中试试下面的例子：
x = 5
if
x == 5:
print
'x is equal to 5.'
你看到了什么？
x == 5
返回的是
True
，所以打印出了相应的文字。现在试一下这个：
x = 3
if
x == 5:
print
'x is equal to ...
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