Python Mapping list Learning

List mapping is a very useful way to transform data by applying a function to each element of the list, and you can use a strategy or method to traverse the calculation of each element.

For example:

?

12345678910111213141516171819202122232425262728293031323334

params = {"server":"mpilgrim", \                "database":"master", \                "uid":"sa", \                "pwd":"secret" \                }print ["%s=%s" % (k, params[k]) for k in params.keys()]print ‘;‘.join(["%s=%s" % (k, params[k]) for k in params.keys()])返回结果为：返回结果为：[‘uid=sa‘, ‘pwd=secret‘, ‘database=master‘, ‘server=mpilgrim‘]还可以改进下，把元组转化成字符串，使用join函数方法。‘uid=sa;pwd=secret;database=master;server=mpilgrim‘(join函数不仅使用于元组还使用于列表，功能是字符串化）split跟join相反，把字符串转换成元组看如下应用<pre name="code" class="python">>>> <span style="font-family: Arial, Helvetica, sans-serif;">str = ‘server=mpilgrim;uid=sa;database=master;pwd=secret‘</span></pre>>>> str.split(‘;‘)<br>[‘server=mpilgrim‘, ‘uid=sa‘, ‘database=master‘, ‘pwd=secret‘]<br>>>> str.split(‘;‘, 1)<br>[‘server=mpilgrim‘, ‘uid=sa;database=master;pwd=secret‘]<br>>>> str.split(‘;‘, 2)<br>[‘server=mpilgrim‘, ‘uid=sa‘, ‘database=master;pwd=secret‘]<pre class="brush:java;"></pre><p></p><p><br></p><p><strong>列表映射用例：</strong></p><pre class="brush:java;"><pre class="brush:java;">>>> li = [1, 9, 8, 4]>>> [elem*2 for elem in li] 1[2, 18, 16, 8]>>> li[1, 9, 8, 4]</pre><br><br></pre><br>

Python Mapping list Learning