Hi how do I import files inside a txt file?

[DL Neil]

On 3/09/19 1:48 AM, Spencer Du wrote:
> On Monday, 2 September 2019 15:29:07 UTC+2, Joel Goldstick  wrote:
>> On Mon, Sep 2, 2019 at 9:21 AM Spencer Du <spencerdu at hotmail.co.uk> wrote:
>>>
>>> On Monday, 2 September 2019 15:03:52 UTC+2, Joel Goldstick  wrote:
>>>> On Mon, Sep 2, 2019 at 8:46 AM Spencer Du <spencerdu at hotmail.co.uk> wrote:
>>>>>
>>>>> On Monday, 2 September 2019 13:36:06 UTC+2, Pankaj Jangid  wrote:
>>>>>> Spencer Du <spencerdu at hotmail.co.uk> writes:
>>>>>>
>>>>>>> How do i import files inside a txt file if they exist in the current directory?
>>>>>>>
>>>>>>> Here is the current code but I dont know how to do it correctly.
>>>>>>>
>>>>>>> import paho.mqtt.client as mqtt
>>>>>>> from mqtt import *
>>>>>>> import importlib
>>>>>>> import os
>>>>>>> import os.path
>>>>>>> # from stateMachine import *
>>>>>>>
>>>>>>> with open("list_of_devices.txt", "r") as reader:
>>>>>>>      for item in reader:
>>>>>>>              try:
>>>>>>>                      os.getcwd()
>>>>>>>                      print("hi")
>>>>>>>              except:
>>>>>>>                      print("error")
>>>>>>>
>>>>>>> This is "list_of_devices.txt":
>>>>>>> test1,test2
>>>>>>>
>>>>>>> Each name refers to a python file.
>>>>>>>
>>>>>> My interpretation is that you want to read a file (list_of_devices.txt)
>>>>>> and this file contains names of other files and you want to read those
>>>>>> files as well and do something with them (read or print or whatever).
>>>>>>
>>>>>> You can approach it like this: write a function to read a file and work
>>>>>> on it. Like this,
>>>>>>
>>>>>> def fn(fname):
>>>>>>      with open(fname, "r") as f:
>>>>>>           try:
>>>>>>                  # work with f
>>>>>>           except:
>>>>>>                  print("error")
>>>>>>
>>>>>> Then use this function in your code that you have writen. Like this
>>>>>>
>>>>>> with open("list_of_devices.txt", "r") as reader:
>>>>>>       for item in reader:
>>>>>>           try:
>>>>>>                  fn(item)
>>>>>>           except:
>>>>>>                  print("error")
>>>>>>
>>>>>> In the example that you gave, you have written contents of
>>>>>> "list_of_devices.txt" as
>>>>>>
>>>>>> test1,test2
>>>>>>
>>>>>> Take care to read them as comma separated. Or if you have control then
>>>>>> write them on separate lines.
>>>>>>
>>>>>> Regards.
>>>>>> --
>>>>>> Pankaj Jangid
>>>>>
>>>>> Hi Pankaj
>>>>>
>>>>> I dont understand so what is complete code then?
>>>>>
>>>>> Thanks
>>>>> Spencer
>>>>> --
>>>>> https://mail.python.org/mailman/listinfo/python-list
>>>>
>>>> Pardon me for guessing, but your question seems to imply that you know
>>>> how you want to do something .. but I'm not sure you have tackled your
>>>> problem correctly.
>>>>
>>>> My guess is:  Depending upon the names listed in a text file, you want
>>>> to do different imports into your program.   You don't yet know how to
>>>> read a file with python.
>>>>
>>>> First, when you run your program, python compiles it in order.  Since
>>>> you don't know what you want to import until after you run your
>>>> program, you can't import those modules.  You may be able to run a
>>>> program to read the module list, then have it output to a new file the
>>>> code you eventually want to run based on the modules you discovered.
>>>> That sounds cute in a way, but probably not in a good way.  You could
>>>> also surround import statements with try/except code that will import
>>>> what it can, and alert you when it can't
>>>>
>>>> Can you give us the bigger picture of what you want to accomplish?
>>>> This might lead to a better solution than the one you are thinking of
>>>> now
>>>>
>>>> --
>>>> Joel Goldstick
>>>> http://joelgoldstick.com/blog
>>>> http://cc-baseballstats.info/stats/birthdays
>>>
>>> Hi
>>>
>>> I have a txt file which contains the names of files. They are .py files. I want to import them into a python file if they exists in current directory and if the name of file does not exist then print out error and not import. How do I do this?
>>>
>>> Thanks
>>> Spencer
>>
>> Here is a discussion on Stack overflow that lays out how you can
>> dynamically import files.  This should get you started in the right
>> direction.  First, see if you can write code to read the file, and
>> retrieve the names of the modules you want to import.   Come back if
>> you stumble with your code for that
>>
>> https://stackoverflow.com/questions/301134/how-to-import-a-module-given-its-name-as-string
>>> --
>>> https://mail.python.org/mailman/listinfo/python-list
>>
>>
>>
>> -- 
>> Joel Goldstick
>> http://joelgoldstick.com/blog
>> http://cc-baseballstats.info/stats/birthdays
> 
> Ok I have this code to retrieve the names of modules I want to import. Now how do I check if they exist in current directory and if they exist import them into the python program. Thanks.
> 
> with open("list_of_devices.txt", "r") as f:
> 	for item in f:
> 		print(item)


Perhaps it is time to slow-down and take a breather?

The answer to this step has already been covered in this thread!


Many languages require one to *anticipate* every contingency - anything 
that could go 'wrong'. For example, that a file does not exist and 
cannot be imported.

However, Python follows a philosophy that it is "easier to ask 
forgiveness than it is to get permission"*. In other words, to use the 
try...except construct - in this case, to attempt an import (the "try") 
and if that fails (probably because the file does not exist) then to 
defend/react accordingly (the "except" - "except" = "exception").

In other words, only worry about 'the problem' (post fact), should it 
arise. This works quite neatly for your use-case.


Such is what is called "a Python idiom" - the way things are done in 
Python (which may be fundamentally different from other programming 
language(s) you use). It is a mistake to attempt to 'translate' from one 
programming language into another merely by replacing one "syntax" with 
the other. For example a Python for-loop is actually a 'foreach' 
construct and thus not the same as the C/C++, FORTRAN, BASIC, etc, etc, 
for-loop - no matter what the words say! Learning (and absorbing) idioms 
and language philosophies is what separates better programmers from the 
mediocre!


Are you taking the time to research? Have you reviewed the Python docs*?


If you must check for the presence of a file, entering "python file 
exists" into a search engine produces numbers of 'hits'!

The hard way (the syntax-only 'translation', and non-Pythonic approach), 
is that the PSL offers "11.2. os.path — Common pathname manipulations"*


* WebRefs:
https://en.wikiquote.org/wiki/Grace_Hopper
https://docs.python.org/3.6/index.html [adjust versionNR to suit]
https://stackabuse.com/python-check-if-a-file-or-directory-exists/

-- 
Regards =dn