CODEWITHSUNDEEP
pythonimportduplicatesoutput
saturns
saturns

Reputation: 57

Fix duplicate outputs

I'm trying to run this code, and all seems to be going well, however, the outputs duplicate and I have no clue why. when I remove the check for "main" (the file I'm working in), it doesn't have the same problem and only returns the output once

def file_exists(name):
  try:
    exec("import " + name) 
    return True 
  except ModuleNotFoundError:
    return False

#test
print(file_exists("main")) # -> True (file being worked in)
print(file_exists("module1")) # -> True (module exists in program)
print(file_exists("math")) # -> True
print(file_exists("english")) # -> False

duplicate outputs

Upvotes: 1

Views: 440

Answers (3)

SAJAD
SAJAD

Reputation: 1

OK

1-The problem with running this code too much is that when you import the main file, it causes the main file to run twice.

2-The second problem is that the module1 function is part of the main file and must be imported in this way.

from main import module1

Look at this

def module1():
    pass

def file_exists(name):
  try:
    exec(f"import {name}")
    return name, True
  except:
      try:
        exec(f"from main import {name}")
        return name, True
      except Exception:
        return name, False

files=["main", "module1", "math", "english"]
for f in files:
    print(file_exists(f))

Upvotes: 0

Sai Charan Adurthi
Sai Charan Adurthi

Reputation: 21

Whats happening here is when you include check for "main"

The program runs "import main" in runtime and that actually initialises the main module again

i.e. something like below

def file_exists(name):
try:
    exec("import " + name) 
    return True # return true for initial call,#5. True
except ModuleNotFoundError:
    return False

#test
print(file_exists("main")) # -> True (file being worked in), this imports the module and initialises it as its not found in sys.modules

"""
def file_exists(name):
   try:
       exec("import " + name) - #a duplicate import so executes and moves to next line
       return True #returns true
   except ModuleNotFoundError:
       return False

   #test
   print(file_exists("main")) #1. True
   print(file_exists("module1")) # -> True (module exists in program), 2.True
   print(file_exists("math")) # -> True, 3.True
   print(file_exists("english")) # 4. False
"""

# after 4th print the control goes back to the check which call the import that will print from (5)
print(file_exists("module1")) # -> True (module exists in program), 6. True
print(file_exists("math")) # -> True, 7.True
print(file_exists("english")) # -> False` 8. True

But if we remove check for main none of the above happens and simply 4 checks with one print statement each are executed, thus only 4 lines of print.

Refer - https://docs.python.org/2/reference/simple_stmts.html#the-import-statement

Upvotes: 0

HPKG
HPKG

Reputation: 345

My rough idea is that once main runs, it runs all import statements, then u run import again using exec, the subsequent imports fail due to double import of same module name. I would print the exception seen - including type and message.

Upvotes: 1

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