Python If statement returning invalid syntax when code seems to be correct [on hold]

Python: Python 3.6

I have this code, to create a directory for the year, and a directory in that directory.

def create_dir(year_exists, month_exists):
    year_exists=os.path.isdir((str(datetime.datetime.now().year))
    if year_exists==true:
        os.chdir(str(datetime.datetime.now().year))
    else:
        os.mkdir(str(datetime.datetime.now().year))
        os.chdir(str(datetime.datetime.now().year))
    month_exists=os.path.isdir((str(datetime.datetime.now().month))
    if month_exists==true:
        os.chdir(str(datetime.datetime.now().month))
    else:
        os.mkdir(str(datetime.datetime.now().month))
        os.chdir(str(datetime.datetime.now().month))

And yes, I did import datetime and os.

However, when I run the code, I get

  File "C:\Users\[username]\Desktop\python projects\Python-Stats-Finder\finder.py", line 29
    if year_exists==true:
                        ^
SyntaxError: invalid syntax

What did I do wrong with my code to generate the syntax error, even if the syntax is correct (I checked)?