How can I convert a datetime object to milliseconds since epoch (unix time) in Python?

Broken down: Conversion process

The process of converting a datetime object to Unix time milliseconds involves interacting with the Unix Epoch, a point in time established on January 1, 1970, that forms the basis of Unix time.

Pre-Python 3.3: Old-school conversions

For Python versions prior to 3.3, the to-epoch conversion requires more elaborate steps:

import time
from datetime import datetime

# Oldie but a goodie, like Grandma's cookie recipe
dt = datetime.now()
epoch = datetime.utcfromtimestamp(0)  # The Big Bang of Unix time
delta = dt - epoch  # Time travel to 1970!
milliseconds = int(delta.total_seconds() * 1000)  # Magic happens here
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Timezone games: Aware conversions

For timezone-aware datetime objects, the timestamp() function is your best friend:

from datetime import datetime, timezone

# Spacetime-aware datetime object, in UTC we trust!
dt = datetime.now(timezone.utc)  
milliseconds = int(dt.timestamp() * 1000)  # Easy peasy lemon squeezy
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Micro-measures: Extra precision

If your application demands micrometric precision, include the microseconds in your computations:

from datetime import datetime

dt = datetime.now()
# Milliseconds on steroids, we don't miss even a microsecond
milliseconds = int(dt.timestamp() * 1000) + int(dt.microsecond / 1000)  
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Context matters: Use cases

Timestamp conversions play a crucial role in scenarios such as logging, syncing systems, or whenever high-resolution timestamps are required. Always be aware of entity details like time zones, handling leap seconds, or adjustments due to Daylight Saving Time.

UNIX warriors: Converting seconds

In the heat of the coding moment, you may face a Unix timestamp in seconds requiring transformation to a datetime object or milliseconds:

seconds_since_epoch = 1615423407
milliseconds_since_epoch = seconds_since_epoch * 1000  # Becoming richer, millisecond-wise

# To convert back to a datetime object
dt = datetime.utcfromtimestamp(seconds_since_epoch)  # Back to the future!
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Legacy tales: String formatting

Dusty corners of Python, legacy code might work with a more archaic method:

import datetime

# Vintage conversion, only hipsters use this
milliseconds = int(datetime.datetime.now().strftime("%s")) * 1000  
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This method is not recommended, as it's platform-dependent and lacks forward compatibility.

Library Luxuries: datetime Alternatives

Despite the power and versatility of the datetime module, a few third-party libraries smooth out some of its wrinkles. Align your code to these libraries—Arrow, dateutil, and Delorean—to enjoy the luxury of easy datetime manipulations.

Taking Delorean for a spin:

from delorean import Delorean

d = Delorean()
milliseconds = d.epoch * 1000  # Write code Marty, not dates!
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Consult the relevant docs before using these libraries.