"Python Trick" % locals()

I just learned this python trick for string formatting. Here's an example:

def compileCommand(sourcePath, outputPath):
    switches = "-O0 -g"
    return "gcc -c %(switches)s %(sourcePath)s -o %(outputPath)" % locals()

This trick uses the dict locals() to supply the values for formatting the string with the '%' signs in it. The names inside the parens are resolved with the local variable names in the function.

Example usage of the above function:

cmd = compileCommand("hello.c", "hello.o")
assert cmd == "gcc -c -O0 -g hello.c -o hello.o"