How to determine the first day of a month in Python

>>> from calendar import monthrange
>>> monthrange(2011, 2)
(1, 28)

>>> from calendar import monthrange
>>> monthrange(2012, 2)
(2, 29)

NSLocale *usLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
NSLocale *gbLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"];

NSString *dateFormat;
NSString *dateComponents = @"yMMMMd";

dateFormat = [NSDateFormatter dateFormatFromTemplate:dateComponents options:0 locale:usLocale];
NSLog(@"Date format for %@: %@",
    [usLocale displayNameForKey:NSLocaleIdentifier value:[usLocale localeIdentifier]], dateFormat);

dateFormat = [NSDateFormatter dateFormatFromTemplate:dateComponents options:0 locale:gbLocale];
NSLog(@"Date format for %@: %@",
    [gbLocale displayNameForKey:NSLocaleIdentifier value:[gbLocale localeIdentifier]], dateFormat);

// Output:
// Date format for English (United States): MMMM d, y
// Date format for English (United Kingdom): d MMMM y

from datetime import datetime
import calendar

def get_week_numbers_in_month(year,month):
    ending_day    = calendar.monthrange(year, month)[1] #get the last day of month
    initial_week  = datetime(year, month, 1).isocalendar()[1]
    ending_week   = datetime(year, month, ending_day).isocalendar()[1]
    return range(initial_week, ending_week + 1)

print("Your month contains the following weeks:")
print(get_week_numbers_in_month(2017,10))
# range(39, 45)