human
Solve the following python programming problem given the following code:
def _calculate_sources(self, targets) : 
    sources = set () 
    def collect_sources(target) : 
        if self.is_gentarget (target) : 
            sources.update (target.sources_relative_to_buildroot ()) 
for target in targets : 
        target.walk (self) 
return sources 

    
    

    Fix the buggy line: target.walk (self)
assistant
#Here is Python program to fix the buggy line: target.

target.walk (def collect_sources()