Why can't the import command be found?

Question

I am using the input function from fileinput module to accept script via pipes or input file Here is the minimum script:

finput.py

import fileinput

with fileinput.input() as f:
    for line in f:
        print(line)

After making this script executable, I run ls | ./finput.py and get unexpected error message

./finput.py: line 1: import: command not found
./finput.py: line 3: syntax error near unexpected token `('
./finput.py: line 3: `with fileinput.input() as f:'

The only fix I found is when I add #!/usr/bin/env/python3 before the import statement.

But this issue seems to be related only to the fileinput module. Since the following script worked well without a shebang:

fruit.py

import random

fruits = ["mango", "ananas", "apple"]
print(random.choice(fruits))

Now what am I missing? Why can't the import command be found since the shebang is not required in finput.py?

Answer 1

Your need to tell your OS that this is a Python program, otherwise, it's interpreted as a shell script (where the import command cannot be found).

Like you identified, this is done by using a shebang line:

#!/usr/bin/env python3

---

This is only needed if you are going to run your script like this: ./script.py, which tells your OS "run this executable". Doing so requires that your OS identify how it's supposed to run the program, and it relies on the shebang line for that (among other things).

However if you run python script.py (which I'm guessing you did for fruit.py), then Python does not ask your OS whether that is a Python program or not, so the shebang line doesn't matter.