Draw Control Flow Graph using pycfg | Python

Prerequisites: Control Flow Graph, Cyclomatic Complexity

Usually, we draw manual Control Flow Graph using pen and paper by analyzing the control flow of the program. CFG helps us finding independent paths (Cyclomatic Complexity), which leads to the number of test cases required to test the program. We can automate the CFG task using a Python library called pycfg. This library takes a Python script as input and gives graph as output.

We can use pycfg in 2 following ways

  1. By Directly using the file
  2. By importing library in the program

By Directly using the file

  1. Download pycfg tar file
  2. UnZip it
  3. Use pycfg.py file

Note: pycfg.py file location after unzipping is pycfg-0.1/pycfg/pycfg.py.

Let’s take whiletest.py file to get CFG.





a= 10
while(a <= 0):
    if a == 5:
    a += 1


Run below command on terminal.

python path_to/pycfg.py path_to/whiletest.py -d


This approach gives output in the form of Graph having Nodes, labeled Sentences, edges between nodes.

By importing library in the program

With help of importing linrary and tkinter, we can do way batter than just using pycfg.py file alone.

  • Representing CFG instead of terminal.
  • Find cyclomatic complexity also

Run the below command

sudo pip install pycfg

Once Done, using same whiletest.py for testing. We can run the following python program on whiletest.py.

 python /path_to/this_file.py /path_to/whiletest.py

Below is the code –





from pycfg.pycfg import PyCFG, CFGNode, slurp
import argparse
import tkinter as tk
from PIL import ImageTk, Image
if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('pythonfile', help ='The python file to be analyzed')
    args = parser.parse_args()
    arcs = []
    cfg = PyCFG()
    g = CFGNode.to_graph(arcs)
    g.draw(args.pythonfile + '.png', prog ='dot')
    # Draw using tkinter.
    root = tk.Tk()
    root.title("Control Flow Graph")
    img1 = Image.open(str(args.pythonfile) + ".png"# PIL solution
    img1 = img1.resize((800, 600), Image.ANTIALIAS)
    img = ImageTk.PhotoImage(img1)
    background ="gray"
    panel = tk.Label(root, height = 600, image = img)
    panel.pack(side = "top", fill ="both", expand = "yes")
    nodes = g.number_of_nodes()     # no. of nodes.
    edges = g.number_of_edges()     # no. of Edges.
    complexity = edges - nodes + 2         # Cyclomatic complexity
    frame = tk.Frame(root, bg = background)
    frame.pack(side ="bottom", fill ="both", expand = "yes")
    tk.Label(frame, text ="Nodes\t\t"+str(nodes), bg = background).pack()
    tk.Label(frame, text ="Edges\t\t"+str(edges), bg = background).pack()
    tk.Label(frame, text ="Cyclo Complexity\t"+
             str(complexity), bg = background).pack()



Reference: https://pypi.org/project/pycfg/

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