Python notes

Python notes

### Handling error example 

import sys
import traceback

try:
    f = open('myfile.txt')
    s = f.readline()
    i = int(s.strip())
except OSError as err:
    print("OS error: {0}".format(err))
except ValueError:
    print("Could not convert data to an integer.")
except:
    print("Unexpected error:", sys.exc_info()[0]) #print type of exception
    traceback.print_exc() #print the whole traceback stack
    # raise ## raise exception to higher stack if necessary
finally:
    # command will always run, regardless of the exception. 

### refer: https://docs.python.org/3.7/tutorial/errors.html



### Run function inside a python file directly
def myfunction():
    ...

if __name__ == '__main__':
    globals()[sys.argv[1]]()
    
python myscript.py myfunction

This works because you are passing the command line argument (a string of the function's name) into  locals, a dictionary with a current local symbol table. The parantheses at the end will make the function be called.

update: if you would like the function to accept a parameter from the command line, you can pass in sys.argv[2] like this:

def myfunction(mystring):
    print mystring

if __name__ == '__main__':
    globals()[sys.argv[1]](sys.argv[2])
This way, running python myscript.py myfunction "hello" will output hello.

### Refer: https://stackoverflow.com/questions/3987041/run-function-from-the-command-line