Python logging-module that writes to both the console and a file

Question

I've created a small module with a function plog() that allows to easily print to both a log file and the console. It also creates a directory "log" at the location of the file that imports the module. Although I'm quite a beginner in terms of Python I'm not satisfied with my code since I'm using two global variables. I need those, because they store the name of the last file and function that called plog(). So could you guys give me recommendations how I could improve the code and make it more 'pythonic'? This is my code so far:

import datetime
import inspect
import os
print("Setting up logfile via very_nice_log.py")
# create name of log file via datetime
log_file_name = str(datetime.datetime.now())[:-9]
log_file_name = log_file_name.replace("-", "")
log_file_name = log_file_name.replace(" ", "")
log_file_name = log_file_name.replace(":", "")
# check if it is possible to get the path of the file that called very_nice_log
if len(inspect.stack()[1:]) == 0:
 print("WARNING: could not locate file that called very_nice_log")
# get path of the file that imported very_nice_log
for frame in inspect.stack()[1:]:
 if frame.filename[0] != '<':
 log_path = "/".join(frame.filename.split("/")[:-1])
 print("Log path is " + log_path)
 break
log_path = log_path + "/log"
# check if there is a directory called "log", create one if not
if not os.path.isdir(log_path):
 os.mkdir(log_path)
# create log file
print(log_path + "/" + log_file_name + ".txt")
log_file = open(log_path + "/" + log_file_name + ".txt", "w+")
print("Created log file")
log_file.write("Starting to log...\n\n")
# set up 2 variables to store the last function and file that called plog()
last_func_name = ""
last_module_name = ""
# define a function that prints to both the log file and the console
def plog(amk):
 # set those variables to global to store the names of the last file and function
 global last_func_name
 global last_module_name
 # print the string to console
 print(amk)
 # get the name and function that called plog()
 module_name = (inspect.stack()[1][1].split("/")[-1])[:-3]
 func_name = inspect.stack()[1][3]
 # if plog is not called from a function, set function name to "main"
 if func_name == "<module>":
 func_name = "main"
 # if file or function has changed since last time plog got called, write a seperator
 if module_name != last_module_name:
 log_file.write("=====================================================================\n")
 elif func_name != last_func_name:
 log_file.write("---------------------------\n")
 # write to log file
 log_file.write(str(datetime.datetime.now())[:-7] + ": " + module_name + ": " + func_name + ": " + amk + "\n")
 # update the names of last file and function
 last_func_name = func_name
 last_module_name = module_name

edit: Usage Simply write

from very_nice_log import plog
plog("foo")

in another python file.

This is an example output to the log file. 2 files hello.py and testing2.py were used:

Starting to log...
=====================================================================
2019年06月09日 16:51:02: hello: main: Amk1
2019年06月09日 16:51:02: hello: main: amk2
---------------------------
2019年06月09日 16:51:02: hello: func1: func1mak
2019年06月09日 16:51:02: hello: func1: func1mak
---------------------------
2019年06月09日 16:51:02: hello: func2: func2amk
---------------------------
2019年06月09日 16:51:02: hello: func1: func1mak
=====================================================================
2019年06月09日 16:51:02: testing2: func45: amkanderesfile
2019年06月09日 16:51:02: testing2: func45: amkanderesfile
=====================================================================
2019年06月09日 16:51:02: hello: func1: func1mak
=====================================================================
2019年06月09日 16:51:02: testing2: func45: amkanderesfile
---------------------------
2019年06月09日 16:51:02: testing2: func46: yoyoyo
2019年06月09日 16:51:02: testing2: func46: yoyoyo
---------------------------
2019年06月09日 16:51:02: testing2: func45: amkanderesfile

As you can see it nicely separates the log-file into section between different files and functions. I'm very happy with this but as I said, I'm a bit concerned about the quality of my code. Especially the global variables seem to be a bad solution. So what would you guys change and why? I am very curious about your suggestions and would love to learn how to write better code.

Best, Tobi

• random_npc: Idk about you...but the code already seems beautiful...I was just searching for a logger...more than happy to find one...the output looks pretty neat...thanks
• Peilonrayz: Do you know about the logging library? If you don't want an answer to be "Try usinglogging" you should tag this with reinventing-the-wheel.
• eto3542: @Peilonrayz alright, I've added the tag. I know about the logging-library but to be honest I preferred to write my own code instead of trying to understand the library
• QuantumChris: Generally when I write a custom logger, I will use a decorator. These are great because they just wrap around any function/method call and can tell you about state; capture errors; print to files etc. There will also be ways around using globals by capturing what you need from the function you're decorating.

Answer 1

Some suggestions:

• You could use str(datetime.date.today()) to get the current date.

• You can chain replace calls:

  >>> 'abba'.replace('a', 'c').replace('b', 'd')
  'cddc'
  

• if len(inspect.stack()[1:]) == 0: would usually be replaced with just if inspect.stack()[1:].
• Treating your variables as immutable makes the code much easier to read. For example, log_path = "/".join(frame.filename.split("/")[:-1]) + "/log" means you only have to understand one assignment rather than the connection between two of them.
• os.makedirs takes an option so you don't have to check whether the directory exists already.
• String concatenation using + is discouraged for anything more than two strings. Probably the best solution available today is f-strings. For example, log_path + "/" + log_file_name + ".txt" would become f"{log_path}/{log_file_name}.txt".
• I don't understand the name amk. Names are incredibly important for the maintainability of your code, but I don't know what to suggest as a replacement except possibly message.
• You could put the globals into fields in a class; that way they would be kept between invocations without polluting the main namespace.

Answer 2

To expand on l0b0's answer:

• Don't chain str.replace's for the same reason you don't concatenate strings. If you need to perform multiple translations at the same time instead use str.maketrans and str.translate.

  >>> table = str.maketrans('ab', 'cd', 'e')
  >>> 'abeeba'.translate(table)
  'cddc'
  

• Your code only supports Unix paths, this means it doesn't work on Windows. To fix this change all of your '/' to os.sep.

• Rather than manual string file handling, you should use pathlib.

  # From
  "/".join(frame.filename.split("/")[:-1])
  logpath + os.sep + "log"
  # To
  pathlib.Path(frame.filename).parent
  logpath / "log"
  

• Add some more function calls. With good names they should remove your comments.
• You have two quite large bugs with log_path generation. Firstly if the inspect.stack()[1:] is empty or all the file names start with '<' your code results in a NameError. The second won't even print the warning.
• If you can't create the log file, you can always default to os.devnull or some other reasonable default.

import datetime
import inspect
import os
import pathlib
print("Setting up logfile via very_nice_log.py")
def get_datetime_file_name():
 table = str.maketrans(None, None, "- :")
 return (
 str(datetime.datetime.today()).translate(table)
 + '.txt'
 )
def get_log_path():
 for frame in inspect.stack()[1:]:
 if frame.filename[0] != '<':
 return pathlib.Path(frame.filename).parent
 print("WARNING: could not locate file that called very_nice_log")
 return None
def make_log_file():
 log_path = get_log_path()
 if log_path is None:
 return open(os.devnull, "w")
 log_path /= "log"
 log_path.mkdir(parents=True, exists_ok=True)
 log_path /= get_datetime_file_name()
 print(str(log_path))
 return log_path.open("w+")
print("Created log file")
log_file = make_log_file()
log_file.write("Starting to log...\n\n")