I am doing a simple project on my Pycharm IDE.
My code is this:
import webbrowser
import time
socialMediaUrls = ["www.google.com","www.edureka.com"]
techUrls = ["www.udacity.com","www.dailymotion.com"]
def open_tabs(url_list):
for element in url_list:
webbrowser.open_new_tab(element)
def main():
webbrowser.open("www.youtube.com",new=0,autoraise=false)
time.sleep(1)
open.tab(socialMedialUrls)
open_tabs(techUrls)
main()
but after running I am getting this message:
C:\Users\adc\AppData\Local\Programs\Python\Python36-32\python.exe
C:/Users/adc/PycharmProjects/untitled1/ur.py
Process finished with exit code 0
And I am getting same message for all my projects. What should I do?
You should call main in that way:
def main():
webbrowser.open("www.youtube.com",new=0,autoraise=false)
time.sleep(1)
open.tab(socialMedialUrls)
open_tabs(techUrls)
if __name__ == "__main__":
main()
Also I see that your code contains some other errors. For example, in Python there is False keyword, not false. Lines with open.tab and open_tabs will not work too.
Currently, no instructions are reachable in your script (besides the import statements)
in:
def main():
webbrowser.open("www.youtube.com",new=0,autoraise=false)
time.sleep(1)
open.tab(socialMedialUrls)
open_tabs(techUrls)
main()
indentation suggests that you're performing a recursive call (which isn't what you want).
Unindent main() to make sure you execute something in your script.
Or put the instructions of main at zero-indent level outside any procedure (in that case, it is executed even when importing the module, probably not important here)
(note that python programs don't need a main(), this isn't C)
Related
I have this code:
import sys
def random(size=16):
return open(r"C:\Users\ravishankarv\Documents\Python\key.txt").read(size)
def main():
key = random(13)
print(key)
When I try running the script, there are no errors, but nothing appears to happen. I expected it to print some content from the key file, but nothing is printed.
What is wrong? How do I make the code run?
You've not called your main function at all, so the Python interpreter won't call it for you.
Add this as the last line to just have it called at all times:
main()
Or, if you use the commonly seen:
if __name__ == "__main__":
main()
It will make sure your main method is called only if that module is executed as the starting code by the Python interpreter. More about that here: What does if __name__ == "__main__": do?
If you want to know how to write the best possible 'main' function, Guido van Rossum (the creator of Python) wrote about it here.
Python isn't like other languages where it automatically calls the main() function. All you have done is defined your function.
You have to manually call your main function:
main()
Also, you may commonly see this in some code:
if __name__ == '__main__':
main()
There's no such main method in python, what you have to do is:
if __name__ == '__main__':
main()
Something does happen, it just isn't noticeable
Python runs scripts from top to bottom. def is a statement, and it executes when it is encountered, just like any other statement. However, the effect of this is to create the function (and assign it a name), not to call it. Similarly, import is a statement that loads the other module (and makes its code run top to bottom, with its own global-variable context), and assigns it a name.
When the example code runs, therefore, three things happen:
The code for the sys standard library module runs, and then the name sys in our own module's global variables is bound to that module
A function is created from the code for random, and then the name random is bound to that function
A function is created from the code for main, and then the name main is bound to that function
There is nothing to call the functions, so they aren't called. Since they aren't called, the code inside them isn't run - it's only used to create the functions. Since that code doesn't run, the file isn't read and nothing is printed.
There are no "special" function names
Unlike in some other languages, Python does not care that a function is named main, or anything else. It will not be run automatically.
As the Zen of Python says, "Explicit is better than implicit". If we want a function to be called, we have to call it. The only things that run automatically are the things at top level, because those are the instructions we explicitly gave.
The script starts at the top
In many real-world scripts, you may see a line that says if __name__ == '__main__':. This is not "where the script starts". The script runs top to bottom.
Please read What does if __name__ == "__main__": do? to understand the purpose of such an if statement (short version: it makes sure that part of your top-level code is skipped if someone else imports this file as a module). It is not mandatory, and it does not have any kind of special "signalling" purpose to say where the code starts running. It is just a perfectly normal if statement, that is checking a slightly unusual condition. Nothing requires you to use it in a script (aside from wanting to check what it checks), and nothing prevents you from using it more than once. Nothing prevents you from checking whether __name__ is equal to other values, either (it's just... almost certainly useless).
You're not calling the function. Put main() at the bottom of your code.
I have the following structure in code.
In main.py:
def run(parameters):
# do something
In execution.py:
import main
if __name__ = "main":
main.run(parameters)
However, I get the following error - main has no 'run' member.
When I run that code there is no output, because the test in execution.py should be if __name__ == "__main__":. The if-test in your code is never true.
Buy when I fix that problem, main.run() executes as expected, but only if I fix another problem. The function body of run() must consist of more than a comment. You need pass at the very least.
So that is a syntax error, which means that the def statement doesn't actually define the function. Which explains the message.
This question already has answers here:
Why doesn't the main() function run when I start a Python script? Where does the script start running (what is its entry point)?
(5 answers)
Closed 6 years ago.
I am writing a simple Python program with some functions, one of which is a main() function executes the other functions. However when I run the code below there is no output. Can someone tell me if they see an error in the structure?
def print1():
print("this is also a function")
def print2():
print("this is a function")
def main():
print1()
print2()
You need to call main(). Right now it is just a definition. What use is an entry in a dictionary if nobody uses the word?
def print1():
print("this is also a function")
def print2():
print("this is a function")
def main():
print1()
print2()
main()
It is common in Python programs to do things differently depending on if the file is being imported or run. When a file is executed, the __name__ variable is set either to '__main__' or the name of the file. It is set to '__main__' if the file is being executed as a python script, and it is set to the name of the file if it is being imported. You can use this information so that you don't actually run anything if it is just being imported instead of being run as a python script:
if __name__ == '__main__':
main()
That way, you can import the module, and use the functions without main() being called. If it is run as a python script, however, main() will be called.
Add this to the bottom of your code.
if __name__ == "__main__":
main()
See https://docs.python.org/2/library/main.html
Main needs to be called explicitly. You can do it without the if statement, but this allows your code to be either a module or a main program. If it is imported as a module, main() won't be called. If it is the main program then it will be called.
You are thinking like a C programmer. In this case python acts more like a shell script. Anything not in a function or class definition will be executed.
You need to call main() in order for it to run.
I believe what you mean to be doing is
def print1():
print("this is also a function")
def print2():
print("this is a function")
if __name__ == '__main__':
print1()
print2()
Call this script something.py and then run python something.py from your command line.
I'm trying to use warnings.simplefilter to display my warning once. I've created a subclass to DeprecationWarning. I tried putting the simplefilter in the same module as my warning, and in the package level init as far to the top I could but it will always display the warning on every call. Tested in python 3.4.
my warning:
class MyDeprecationWarning(DeprecationWarning):
pass
how I'm calling simplefilter:
warnings.simplefilter('once', MyDeprecationWarning)
how I'm calling warn:
warnings.warn("Warning!", MyDeprecationWarning)
What's the issue?
If your program is running multiple times or some code in running in a separate process, you may have not issued your commands in the right order. The following program works as expected.
import warnings
class MyDeprecationWarning(DeprecationWarning):
pass
def main():
print('Program Starting')
warnings.simplefilter('once', MyDeprecationWarning)
for _ in range(100):
warnings.warn('Warning!', MyDeprecationWarning)
print('Program Finished')
if __name__ == '__main__':
main()
I have this code:
import sys
def random(size=16):
return open(r"C:\Users\ravishankarv\Documents\Python\key.txt").read(size)
def main():
key = random(13)
print(key)
When I try running the script, there are no errors, but nothing appears to happen. I expected it to print some content from the key file, but nothing is printed.
What is wrong? How do I make the code run?
You've not called your main function at all, so the Python interpreter won't call it for you.
Add this as the last line to just have it called at all times:
main()
Or, if you use the commonly seen:
if __name__ == "__main__":
main()
It will make sure your main method is called only if that module is executed as the starting code by the Python interpreter. More about that here: What does if __name__ == "__main__": do?
If you want to know how to write the best possible 'main' function, Guido van Rossum (the creator of Python) wrote about it here.
Python isn't like other languages where it automatically calls the main() function. All you have done is defined your function.
You have to manually call your main function:
main()
Also, you may commonly see this in some code:
if __name__ == '__main__':
main()
There's no such main method in python, what you have to do is:
if __name__ == '__main__':
main()
Something does happen, it just isn't noticeable
Python runs scripts from top to bottom. def is a statement, and it executes when it is encountered, just like any other statement. However, the effect of this is to create the function (and assign it a name), not to call it. Similarly, import is a statement that loads the other module (and makes its code run top to bottom, with its own global-variable context), and assigns it a name.
When the example code runs, therefore, three things happen:
The code for the sys standard library module runs, and then the name sys in our own module's global variables is bound to that module
A function is created from the code for random, and then the name random is bound to that function
A function is created from the code for main, and then the name main is bound to that function
There is nothing to call the functions, so they aren't called. Since they aren't called, the code inside them isn't run - it's only used to create the functions. Since that code doesn't run, the file isn't read and nothing is printed.
There are no "special" function names
Unlike in some other languages, Python does not care that a function is named main, or anything else. It will not be run automatically.
As the Zen of Python says, "Explicit is better than implicit". If we want a function to be called, we have to call it. The only things that run automatically are the things at top level, because those are the instructions we explicitly gave.
The script starts at the top
In many real-world scripts, you may see a line that says if __name__ == '__main__':. This is not "where the script starts". The script runs top to bottom.
Please read What does if __name__ == "__main__": do? to understand the purpose of such an if statement (short version: it makes sure that part of your top-level code is skipped if someone else imports this file as a module). It is not mandatory, and it does not have any kind of special "signalling" purpose to say where the code starts running. It is just a perfectly normal if statement, that is checking a slightly unusual condition. Nothing requires you to use it in a script (aside from wanting to check what it checks), and nothing prevents you from using it more than once. Nothing prevents you from checking whether __name__ is equal to other values, either (it's just... almost certainly useless).
You're not calling the function. Put main() at the bottom of your code.