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Formatting Dates

When printed, datetimes default to a format like the following: Sun Jan 1 00:00:00 TZ 2018. However, this can be manipulated by using special characters in the system.date.format function:

rightNow = system.date.now()

# Demonstrating the standard format.
print rightNow

# Demonstrating the modified format.
print system.date.format(rightNow, "yyyy-MM-dd HH:mm:ss")

Date Arithmetic

The system.date.add* functions can be used to add to or subtract some amount of time from a date. See the system.date.add* functions for more information.

# Get the current datetime.
newDate = system.date.now()

# Change the time on the new date to 30 minutes ago.
print system.date.addMinutes(newDate, -30)

Date Formatting Characters

The following is a reference of date formatting characters that can be used by system.date.format or Java's DateFormat class. Additionally, there are many other non-scripting uses in Ignition (such as the Vision - Calendar component's Format String property) that can utilize this reference. 

Java's Calendar Class

Java's Calendar Class

Creating Dates

To create an arbitrary date, you can use the java.util.Calendar class. It has various functions to alter the calendar fields, like Calendar.HOUR, Calendar.MONTH, and so on. After you're done manipulating the Calendar, you can use its getTime() function to retrieve the Date represented by the calendar. It also has a handy set() function that takes the common parameters of a Date. The one major "gotcha" here is that January is month zero, not month one. For example:

from java.util import Calendar
cal = Calendar.getInstance()

# set year, month, day, hour, minute, second in one call
# This sets it to Feb 25th, 1:05:00 PM, 2010
cal.set(2010, 1, 25, 13, 5, 0)
myDate = cal.getTime()

Date Arithmetic

Often you'll have a Date object from a component like the Popup Calendar and want to alter it programmatically. Say, subtracting 8 hours from it, or something like that. The java.util.Calendar class is used for this as well. Following the example above, this code would subtract 8 hours from the variable myDate.

from java.util import Calendar
cal = Calendar.getInstance()
cal.setTime(myDate)
cal.add(Calendar.HOUR, -8)
myNewDate = cal.getTime()

Python's Time and Datetime Libraries

Many components in Ignition that contain a Date property actually expect a Java calendar object. Creating a datetime object using Python's built-in libraries and passing them to a date property on a component will result in an exception.

As a result, it

Note_friendly
Title Ignition's System Functions vs Python's Libraries
It is highly recommended to use Ignition's built-in system.date functions.

Creating Dates - Python's Time Library

The time library can be use to return dates as well as time. Times are created as a tuple of integers. The integers represent the following values: year, month, day of the month, hour, minute, second, weekday, day of the year, daylight savings time)

Check out Python's time library documentation for more information. 

import time

# Finds the current local time. The time is returned as a tuple of integers.
myTime = time.localtime()

# Print the time into a 24-character string with the following format: Sun Nov 20 12:00:00 2017
print time.asctime(myTime)

# Alternatively, we can reformat the time in a custom manner, then print it
print time.strftime('%H:%M:%S %b %d %Y', myTime)

Creating Dates - Python's Datetime Library

Python's datetime library offers a bit more flexibility since arithmetic can easily be applied. Additional information on the datetime library can be found in Python's official documentation. 

Note Notice the double use of 'datetime' in the example below. This is because the 'datetime' library has a class named 'datetime.'

import datetime

# Returns the current datetime. 
print datetime.datetime.now()

However, we can clean up the above by importing in the datetime class from the library:

# Imports the class named 'datetime' from the 'datetime' library, so we don't have to state it twice. 
from datetime import datetime

# Returns the current datetime. 
print datetime.now()

If you need to create a specific datetime, instead of just using the current, you can pass in the values directly when creating an instance of datetime:

from datetime import datetime

# Prints out the following datetime: 2018-01-02 03:04:05.000006 
print datetime(2018,1,2,3,4,5,6)

Finding the difference between two datetime objects can easily be accomplished by using the '-' character

from datetime import datetime

rightNow = datetime.now()
someTime = datetime(2018,1,1,1,1,1,1)

# Find the difference between the two dates. 
print someTime - rightNow

Date Arithmetic

With Python's built-in libraries, the timedelta class provides the simplest way to perform arithmetic on a date: It simply creates an object that effectively represents a duration. The duration can then be applied to a datetime. 

# We're including the timedelta class here
from datetime import datetime, timedelta

rightNow = datetime.now()

# Creating a timedelta object, and setting the hours to 8
offset = timedelta(hours = 8)

# Print the current time, and then print the time minus the offset. 
print rightNow
print rightNow - offset