[Python编程(第4版)].(Programming.Python.4th.Edition).Mark.Lutz.文字版

num.display() # num saves the C++ 'this' pointer

num.sub(2)

num.display()

res = num.square() # converted C++ int return value

print('square: ', res)

num.data = 99 # set C++ data member, generated __setattr__

val = num.data # get C++ data member, generated __getattr__

print('data: ', val) # returns a normal Python integer object

print('data+1: ', val + 1)

num.display()

print(num) # runs repr in shadow/proxy class

del num # runs C++ destructor automatically

Because the C++ class and its wrappers are automatically loaded when imported by

the number.py shadow class module, you run this script like any other:

.../PP4E/Integrate/Extend/Swig/Shadow$ python main.py

Number: 1

add 4

Number=5

sub 2

Number=3

square: 9

data: 99

data+1: 100

Number=99

<number.Number; proxy of <Swig Object of type 'Number *' at 0x7ff4bb48> >

~Number: 99

Much of this output is coming from the C++ class’s methods and is largely the same

as the main.cxx r e s u l t s s h o w n i n Example 20-16 (less the instance output format—it’s

a Python shadow class instance now).

Using the low-level extension module

SWIG implements integrations as a C++/Python combination, but you can always use

the generated accessor functions module if you want to, as in Example 20-20. This

version runs the C++ extension module directly without the shadow class, to demon-

strate how the shadow class maps calls back to C++.

Example 20-20. PP4E\Integrate\Extend\Swig\Shadow\main_low.py

"""

run similar tests to main.cxx and main.py

but use low-level C accessor function interface

"""

from _number import * # c++ extension module wrapper

num = new_Number(1)

Number_add(num, 4) # pass C++ 'this' pointer explicitly

1508 | Chapter 20: Python/C Integration

Do

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