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I'm trying to use flask and python. I did a simple file named hello.py . tHis file contains this code:

from flask import Flask
app = Flask(__name__)
@app.route("/")
def main():
    return "Welcome!"
if __name__ == "__main__":
    app.run()
This is a simple hello world with flask. I want to execute it but actually, I have a problem. In the terminal, I typed python hello.py 
and I get this error:
File "hello.py", line 1, in <module>
from flask import Flask
ImportError: No module named flask
Even that I installed flask globally.
I understand that this is a basic question, but I'm stuck?
                Had this before, have you got more than one instance of python running? Sometimes Flask installs in 3 for example but the terminal/command line is in 2 etc
– Daniel Casserly
                Jan 14, 2016 at 10:12
                Please run python -m pip list? Is Flask listed? If not, run python -m pip install flask.
– dirn
                Jan 14, 2016 at 12:44
                I'm not sure since OP said: Even that I installed flask globally. I understand that this is a basic question, but I'm stuck?
– Remi Guan
                Jan 14, 2016 at 9:46
Make sure that you entered the correct entry into the requirements.txt file. It should not be blank.
enter Flask==2.0.0 into the requirements.txt file.
                Rather than editing the requirements.txt file manually, it should be auto-generated it so that you are sure it matches your current environment. See Automatically create requirements.txt
– Gino Mempin
                May 12, 2021 at 23:37
pip install flask
Still you are having the same error then you have more than one version of python installed in your machine. So better to create a virtual environment for your app and install all package in it. For that install virtual environment.
py -m pip install --user virtualenv
Activate your venv by
.\venv\Scripts\activate.bat
Now try to install flask in the venv
python -m virtualenv venv
if you install the flask and still get the error. Then, You should activate the source by following:
source env/bin/activate
                This solution is already provided in another answer. If you have any different solution please mention it. If there is any change/extension required to the original answer, then edit it.
– Azhar Khan
                Dec 17, 2022 at 8:11
        
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