Python Basics--08 Iterations & List Generation

1. Iteration 1.1 Features

In Python, an iteration is done through a for ... in.

Python's for loop can be used not only on a list or a tuple, but also on any other object that can iterate

A For loop can work on an iterative object far more than List,tuple,str,unicode,dict, and if an object says it can iterate, then we iterate it directly with a for loop .

The iterative operation is for a collection, regardless of whether the collection is ordered or unordered, we can always use the for loop to sequentially remove each element of the collection

1.2 Iteration Objects

A collection is a data structure that contains a set of elements that we have covered:

ordered set : List,tuple,str and Unicode;

Unordered collection : Set

unordered collection and has Key-value Yes : dict

1.3 Index iterations

In 1.3.1Python, iterations are always taken out of the element itself, not the index of the element

1.3.2 using the Enumerate () function , we can simultaneously bind indexes index and element name in the For Loop.

1.3.3enumerate () function put: [' Adam ', ' Lisa ', ' Bart ', ' Paul ']

became similar: [(0, ' Adam '), (1, ' Lisa '), (2, ' Bart '), (3, ' Paul ')]

Therefore,each element of the enumerate () iteration is actually a tuple

1.3.4 Example

>>> l=[' Adam ', ' Lisa ', ' Bart ', ' Paul '

>>> for Index,name in Enumerate (L):

... print index, '-', name

...

0-adam

1-lisa

2-bart

3-paul

2. List-Generated

[x * x for x in range (1, one)] <==> [variable arithmetic expression for variable in iterator]

[x * x for x in range (1, one) if x% 2 = 0] <==> [variable arithmetic expression for variable in iterator if filter condition]

[M + N for m in ' ABC ' for n in ' 123 '] <==> [multivariable arithmetic expression for variable 1 in iterator 1 for variable 2 in iterator 2]

[X*y for x, y in Zip (range (1,100,2), Range (2,100,2))] <==> [multivariable arithmetic expression for variable 1, variable 2,... in iterator ( iterator element is tuple )]

[Generate_tr (Name,score) for name, score in D.iteritems ()] <==> [ multivariate function to make arguments call for variable 1, variable 2,... in iterator ( element to tuple )]

2.1 List-generated

2.1.1 Concept

[x * x for x in range (1, 11)]

Equivalent to

>>> L = []

>>> for x in range (1, 11):

... L.append (x * x)

2.1.2 Example

Please use list generation to generate list [1x2, 3x4, 5x6, 7x8, ..., 99x100]

[X*y for x, y in Zip (range (1,100,2), Range (2,100,2))]

2.2 List-generation with conditional filtering

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

>>> [x * x for x in range (1, 11)]

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

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

>>> [x * x for x in range (1, one) if x% 2 = = 0]

[4, 16, 36, 64, 100]

2.3 Nested List-generated

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 for m in ' ABC ' for n ' 123 ']

[' A1 ', ' A2 ', ' A3 ', ' B1 ', ' B2 ', ' B3 ', ' C1 ', ' C2 ', ' C3 ']

The Loop code is translated as follows:

L = []

For M in ' ABC ':

For-N in ' 123 ':

L.append (M + N)

2.4 Formatting strings + complex list generation

2.4.1 thought

Complex, regular strings can be generated using functions

2.4.2 Example

In the resulting table, mark the score red for those who have not passed.

Hint: Red can be implemented with <TD style= "color:red" >.

D = {' Adam ': +, ' Lisa ': $, ' Bart ': 59}

# Generate Table Property string method

def generate_tr (name, score):

If score<=60:

Return ' <tr><td style= ' color:red >%s</td><td>%s</td></tr> '% (name, score)

Return ' <tr><td>%s</td><td>%s</td></tr> '% (name, score)

TDS = [Generate_tr (name,score) for name, score in D.iteritems ()]

print ' <table border= ' 1 "> '

print ' <tr><th>Name</th><th>Score</th><tr> '

print ' \ n '. Join (TDS)

print ' </table> '

Python Basics--08 Iterations & List Generation