How do I echo a variable into a file using python

I was writing a script to go with my homemade smart home network and I came upon a problem storing variables in a file. Here is an abridged version of the code

import datetime
import os

log = open('log.txt')

def timestamp():
    errortime = ('Timestamp: {:%Y-%m-%d %H:%M:%S}'.format(datetime.datetime.now()))
    return str(errortime)

def errormessage():
    //code

def consolelog():
    log.write('Timestamp: ' + timestamp())
    log.write('Error Type: ' + errormessage())
    log.write('------------------')

try:
    prit('hello')
except:
    consolelog()
    print('done')

The code is meant to try the code 'prit('hello') which would come back as a syntax error thus storing the variable(errortype) as Syntax Error. After this I was trying to insert a timestamp and the error type variable into a log.txt file which was returning the following error:

log.write('Timestamp: ' + timestamp())
can only concatenate str (not "NoneType") to str

can anyone explain a way to input variables into a file without receiving a TypeError?

import datetime
import os

log = open('log.txt', 'w')


def timestamp():
    errortime = (
        'Timestamp: {:%Y-%m-%d %H:%M:%S}'.format(datetime.datetime.now()))
    print(errortime)
    errortime = str(errortime)
    return errortime


def errormessage(e):
    errortype = ''
    if isinstance(e, OSError):
        errortype = ('OSError')
    elif isinstance(e, SyntaxError):
        errortype = ('SyntaxError')
    elif isinstance(e, AssertionError):
        errortype = ('AssertionError')
    elif isinstance(e, NameError):
        errortype = 'NameError'

    return errortype


def consolelog(e):
    log.write('Timestamp: ' + timestamp())
    log.write('Error Type: ' + errormessage(e))
    log.write('------------------')


try:
    prit('hello')
except Exception as e:
    consolelog(e)
    print('done')