Python: Simple way to cache function result using decorator

cache.py

#!/usr/bin/python

def cache(func):
    def wrapper(*args, **kwargs):
        if hasattr(func, "cache"):
            return func.cache
        func.cache = func(*args, **kwargs)
        return func.cache
    return wrapper

@cache
def myfun(myvar, mykey = "myval"):
    return myvar, mykey

print(myfun("val1", mykey = "keyval1"))
print(myfun("val2", mykey = "keyval2"))

# OUTPUT:
#     ('val1', 'keyval1')
#     ('val1', 'keyval1')

cache_persistent.py

#!/usr/bin/python

import json
import hashlib
import os

def cache(arg):
    def decorator(func):
        def wrapper(*args, **kwargs):
            func_sig = (func.__module__, func.__name__, args, tuple(sorted(kwargs.items())))

            if persistent:
                cache_dir = '/tmp/cache'
                func_hash = hashlib.sha256(str(func_sig).encode('utf-8')).hexdigest()
                cache_file = os.path.join(cache_dir, func_hash + '.json')
                if not os.path.isdir(cache_dir):
                    os.mkdir(cache_dir, mode = 0o700)

            if not hasattr(func, "cache"):
                func.cache = {}

            if not func_sig in func.cache:
                if persistent:
                    if os.path.isfile(cache_file):
                        with open(cache_file, 'r') as file:
                            func.cache[func_sig] = json.load(file)
                    else:
                        func.cache[func_sig] = func(*args, **kwargs)
                        with open(cache_file, 'w') as file:
                            json.dump(func.cache[func_sig], file)
                else:
                    func.cache[func_sig] = func(*args, **kwargs)

            return func.cache[func_sig]
        return wrapper
    if callable(arg):
        persistent = False
        return decorator(arg)
    else:
        persistent = arg
        return decorator

# Examples

# In memory cache
@cache
def myfun(myvar, mykey = "myval"):
    return myvar, mykey

# Persistent cache
@cache(True)
def myfun2(myvar, mykey = "myval2"):
    return myvar, mykey