Get macro constants from C (++) header file (.h) in Python

Note that there was a peculiar example that "I want to share constants between Python and C ++, I want to fix constants on the C ++ side at compile time, and I want to use the same variables in Python".

Defined in .h from Python

sample.h

#ifndef _PARAM
#define _PARAM

#define NUM 10
#define epoch 100

#endif

Take out a constant like this. This time, global variables defined by const int etc. are not considered because it is troublesome to classify cases.

def read_header_and_get_macro(header_filepath):
    with open(header_filepath, mode='r') as f:
        lst = [s.strip() for s in f.readlines()]
    comment_flg = False
    for l in lst:
        items = l.split()
        if len(items) != 0 and items[0] == "/*":
            comment_flg = True
            continue
        if comment_flg == True:
            if len(items) != 0 and items[0] == "*/":
                comment_flg = False
            continue
        if len(items) < 2 or items[0] != "#define":
            continue
        if items[1] in globals():
            if items[2] == 'true':
                globals()[items[1]] = True
            elif items[2] == 'false':
                globals()[items[1]] = False
            else:
                try:
                    globals()[items[1]] = float(items[2])
                except ValueError:
                    try:
                        globals()[items[1]] = int(items[2])
                    except ValueError:
                        globals()[items[1]] = items[2]

What you are doing

3rd line

    lst = [s.strip() for s in f.readlines()]

Read the file and list it line by line. This time I took a list for each line and turned it in a list, but I am free to turn f.readline () for statement separately

4th line

    comment_flg = False

In C (++), everything from / * to the end with * / is a comment, so a flag to remember this.

6th line

        items = l.split()

Get a list of the contents of the line, which is divided by half-width spaces.

['#define', 'NUM', '10']

I wanted a list like this.

7th line~13th line

        if len(items) != 0 and items[0] == "/*":
            comment_flg = True
            continue
        if comment_flg == True:
            if len(items) != 0 and items[0] == "*/":
                comment_flg = False
            continue

As mentioned above, comments are excluded.

14th line~Line 15

        if len(items) < 2 or items[0] != "#define":
            continue

Lines that do not start with #define are excluded because no macro is defined.

16th line~Line 28

        if items[1] in globals():
            if items[2] == 'true':
                globals()[items[1]] = True
            elif items[2] == 'false':
                globals()[items[1]] = False
            else:
                try:
                    globals()[items[1]] = float(items[2])
                except ValueError:
                    try:
                        globals()[items[1]] = int(items[2])
                    except ValueError:
                        globals()[items[1]] = items[2]

Other than the previous ones should be constants. At this time, ʻitems [1] should contain a constant name, so ʻitems [1] in globals () is used to check if this is defined as a global variable. If it is defined, you can find its value with globals () [items [1]], so if you forcibly rewrite the variable, it will be completed. However, we are processing to align the C ++ bool type to Python, and we are also converting float / int / str.