[Python] TypeError: 'str' object cannot be interpreted as an integer python for loop

My function should return data starting from a given year and given month to today's year and month. I am getting error TypeError: 'str' object cannot be interpreted as an integer

Defining function

def frequency_database(df,start_month,start_year):
data = pd.DataFrame([])
import datetime
start_month=int(start_month)
start_year=int(start_year)
today = datetime.date.today()
today_year=today.strftime('%Y')

for y in range(start_year,today_year):
print('Outer loop enter for year', y)
# Some function...
for x in range(start_month,13):
print('Inner loop enter for month number',x)
# Some function...


Calling funtion

frequency_database(df,1,2015)


Error

TypeError: 'str' object cannot be interpreted as an integer

Stack Trace as requested

---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-37-06567ae5d027> in <module>
12 print('Inner loop enter for month number',x)
13
---> 14 frequency_database(df,1,2015)

<ipython-input-37-06567ae5d027> in frequency_database(df, start_month, start_year)
7 today_year=today.strftime('%Y')
8
----> 9 for y in range(start_year,today_year):
10 print('Outer loop enter for year', y)
11 for x in range(start_month,13):

TypeError: 'str' object cannot be interpreted as an integer

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