python--List-generated--8

Original blog, reprint please indicate the source--Zhou Xuewei http://www.cnblogs.com/zxouxuewei/

I. Build list

To generate list [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], we can use range (1, 11):

>>> Range (1) [123456  789]

But what if you want to generate [1x1, 2x2, 3x3, ..., 10x10]? Method One is the loop:

>>> L = [] for in range (1):     .... *>>> l[149  the  - Bayi []

But the loop is too cumbersome, and the list generation can use a line of statements instead of loops to generate the list above:

 for  in range (1) [14936  []

This is a Python-specific list generation. With list generation, you can generate lists in very concise code.

When writing list generation, put the element x * x to the front, followed by the For loop, you can create a list, very useful, write a few more times, you will soon be familiar with this syntax.

Two. Complex expressions

Iterations that use a for loop can not only iterate through the normal list, but also iterate over the Dict.

Assume the following dict:

' Adam '  the ' Lisa '  - ' Bart '  i}

It can be turned into an HTML table by a complex list-building:

TDS = ['<tr><td>%s</td><td>%s</td></tr>'% (name, score) forName, scoreinchd.iteritems ()]print'<table>'Print'<tr><th>Name</th><th>Score</th><tr>'Print'\ n'. Join (TDS) Print'</table>'

Note: The string can be formatted by%, substituting%s with the specified parameter . The join () method of a string can be used to stitch a list into a string.

Save the printed result as an HTML file, and you'll see the effect in the browser:

<table border="1"><tr><th>name</th><th>score</th ><tr><tr><td>Lisa</td><td></TD></TR><TR><TD >Adam</td><td></td></tr><tr><td>Bart</td><td> </td></tr></table>

Three. Conditional filtering

A list-generated for loop can also be followed by an if judgment . For example:

 for  in range (1) [14936  []

If we want even squares, without changing the range (), you can filter by if:

 for  in range (1if20] [436  [+]

With the IF condition, the current element of the loop is added to the list only if the if is judged to be True.

Four. Multi-layer expressions

For loops can be nested, so in a list build, you can also use a multi-layer for loop to generate the list.

For the string ' ABC ' and ' 123 ', a two-layer loop can be used to generate a full array:

>>> [M + N forMinch 'ABC'  forNinch '123']['A1','A2','A3','B1','B2','B3','C1','C2','C3']

The Loop code is translated as follows:

L = []for in'ABC':    for in ' 123 ' :         + N)

python--List-generated--8