changing variable outside of a function

[tkj80]

Hi,

I have the variable sun_Datetime that was initialized globally outside of 2 user defined functions that I have: 1) get_previous_byday(dayname, start_date=None), 2) date_to_str(day, month, year, sun_dtime).

I tried to access the var sun_Datetime inside date_to_str function and change it.

When sun_Datetime initialized outside of date_to_str function, the variable object id is 54219768. Once within date_to_str function, after calling get_previous_byday function to change the sun_Datetime variable, a new object was created with an different id, 37199768 instead.

I declared sun_Datetime as a global variable, doesn't this allow me to access the original variable, id 54219768 and make changes to it?

import datetime
from datetime import datetime, timedelta
import time

weekdays = ['Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday']

def get_previous_byday(dayname, start_date=None):
    if start_date is None:
        start_date = datetime.today()
    day_num = start_date.weekday()
    day_num_target = weekdays.index(dayname)
    days_ago = (7 + day_num - day_num_target) % 7
    if days_ago == 0:
        days_ago = 7
    target_date = start_date - timedelta(days=days_ago)
    return target_date

def date_to_str(day, month, year, sun_dtime):
    global sun_Datetime
    global sun_Day
    global sun_Month
    global sun_Year
    print("INSIDE date_to_str() function BEFORE get_previous_byday() function call")
    print("variable: [value, type, id] -->", "sun_Datetime passed as sun_dtime: ", [sun_dtime, type(sun_dtime), id(sun_dtime)], "\n")
    sun_dtime = get_previous_byday('Sunday', sun_dtime) ## reference line 4
    print("INSIDE date_to_str() function AFTER get_previous_byday() function call")
    print("variable: [value, type, id] -->", "sun_Datetime passed as sun_dtime: ", [sun_dtime, type(sun_dtime), id(sun_dtime)], "\n")
    day = sun_dtime.day ## reference line 5
    month = sun_dtime.month ## reference line 6
    year = sun_dtime.year ## reference line 7
    sun_Day = str(day)
    sun_Year = str(year)
    if len(str(month)) == 1:
   sun_Month = '0' + str(month)
    else:
   sun_Month = str(month)

sun_Datetime = get_previous_byday('Sunday')
sun_Day = str(sun_Datetime.day) ## reference line 1
sun_Month = str(sun_Datetime.month) ## reference line 2
sun_Year = str(sun_Datetime.year) ## reference line 3

print("BEFORE calling date_to_str() function")
print("variable: [value, type, id] -->", "sun_Datetime: ", [sun_Datetime, type(sun_Datetime), id(sun_Datetime)], "\n")
print("These variables were initialized OUTSIDE of date_to_str() function on reference line 1, 2, 3")
print("variable: [value, type, id] -->", "sun_Day: ", [sun_Day, type(sun_Day), id(sun_Day)])
print("variable: [value, type, id] -->", "sun_Month: ", [sun_Month, type(sun_Month), id(sun_Month)])
print("variable: [value, type, id] -->", "sun_Year: ", [sun_Year, type(sun_Year), id(sun_Year)], "\n")


date_to_str(sun_Datetime.day, sun_Datetime.month, sun_Datetime.year, sun_Datetime)

print("Tried to change the following variables INSIDE date_to_str() function on reference line 4,5,6 and 7")
print("AFTER calling date_to_str() function")
print("variable: [value, type, id] -->", "sun_Datetime: ", [sun_Datetime, type(sun_Datetime), id(sun_Datetime)], "\n")
print("variable: [value, type, id] -->", "sun_Day: ", [sun_Day, type(sun_Day), id(sun_Day)])
print("variable: [value, type, id] -->", "sun_Month: ", [sun_Month, type(sun_Month), id(sun_Month)])
print("variable: [value, type, id] -->", "sun_Year: ", [sun_Year, type(sun_Year), id(sun_Year)], "\n")

Output:
BEFORE calling date_to_str() function
variable: [value, type, id] --> sun_Datetime:  [datetime.datetime(2017, 1, 1, 18, 22, 0, 862455), <class 'datetime.datetime'>, 54219768] 

These variables were initialized OUTSIDE of date_to_str() function on reference line 1, 2, 3
variable: [value, type, id] --> sun_Day:  ['1', <class 'str'>, 37478176]
variable: [value, type, id] --> sun_Month:  ['1', <class 'str'>, 37732000]
variable: [value, type, id] --> sun_Year:  ['2017', <class 'str'>, 37731968] 

INSIDE date_to_str() function BEFORE get_previous_byday() function call
variable: [value, type, id] --> sun_Datetime passed as sun_dtime:  [datetime.datetime(2017, 1, 1, 18, 22, 0, 862455), <class 'datetime.datetime'>, 54219768] 

INSIDE date_to_str() function AFTER get_previous_byday() function call
variable: [value, type, id] --> sun_Datetime passed as sun_dtime:  [datetime.datetime(2016, 12, 25, 18, 22, 0, 862455), <class 'datetime.datetime'>, 37199768] 

Tried to change the following variables INSIDE date_to_str() function on reference line 4,5,6 and 7
AFTER calling date_to_str() function
variable: [value, type, id] --> sun_Datetime:  [datetime.datetime(2017, 1, 1, 18, 22, 0, 862455), <class 'datetime.datetime'>, 54219768] 

variable: [value, type, id] --> sun_Day:  ['25', <class 'str'>, 51992256]
variable: [value, type, id] --> sun_Month:  ['12', <class 'str'>, 37731968]
variable: [value, type, id] --> sun_Year:  ['2016', <class 'str'>, 37478176]