The Line code return Syntax Error with open file

Question

I run a script with the code to open a file and it returns SyntaxError. The script is an open source script that I want to test.

with open(f"/home/mine/myfoldr/myapp.yml", "r") as file:

The line above returns the following error:

File "./startup.py", line 28
    with open(f"/home/mine/myfoldr/myapp.yml", 'r') as file:
                                            ^

I just don't understand what does it mean with f" here, after open(f"...). Because normally it will be write something like below, without f.

with open("/home/mine/myfoldr/myapp.yml", "r") as file:

I think its not a typo because other line code in the script also..have the same style f, for example:

print(f"Which section do you want to change?"
      f"[Application/Controller/Database]")

Does it also throw an error if you remove the f that is before the file name? — Ralf
– Ralf, Commented Sep 6, 2019 at 14:42
it will thrw an error to the next line code that also hav 'f'... thanks — chenoi
– chenoi, Commented Sep 6, 2019 at 14:58

Ralf · Accepted Answer · 2019-09-06 14:50:11Z

2

The f at the start of strings is called f-string, introduced with PEP 489 starting at Python 3.6.

It is used for string formatting, similar to .format(). There are a lot of tutorials on it you can read. The basic example:

x = 22
print('this is {}'.format(x))
print(f'this is {x}')

Here, both lines will output the same resulting string this is 22.

You probably get the error because you are using a version older than Python 3.6, some version where f-strings are not supported.

To test the third-party code you will have to use a newer Python version or modify the code yourself (but this last options may be a lot of work and may introduce some unintentional errors).

answered Sep 6, 2019 at 14:50

Ralf

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5 Comments

chenoi Over a year ago

i tried run the file sudo python3 startup.py and it still return d same... in my env i have python3, 3.5, 3.6 ....

Ralf Over a year ago

@chenoi can you try using python3.6 startup.py?

chenoi Over a year ago

i tried that ..no more syntax error but now got module not found error...for example File "startup.py", line 10, in <module> import mysql.connector ModuleNotFoundError: No module named 'mysql' I tried reinstall again requirements.txt using pip3...but another modulenotfound ModuleNotFoundError: No module named 'pip._internal'

Ralf Over a year ago

@chenoi Careful: for which Python version is pip3 installing the packages? It can be quite messy to use pip when you have more than 1 python version installed

chenoi Over a year ago

Great Ralf.... thanks...for your support and guideline... thanks again... i will try to resolve it....at least i know...d issue is due to my python version that i need to apply 3.6 version

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