What does this python syntax mean?

It picks one of two values based on the boolean outcome.

• ('http://', 'https://') is a tuple
• request.is_secure() produces a boolean result, True or False.
• A boolean is a subclass of int, and True == 1, False == 0.

Thus, if the request was secure (used SSL encryption, over https) the protocol will be set to https:// too.

More recent versions of Python (2.5 and up) allow for a conditional expression, which would be more readable:

protocol = 'https://' if request.is_secure() else 'http://'

This is equivalent to the following

protocol = 'https://' if request.is_secure() else 'http://'

I prefer this to clever indexing tricks.

This just selects 0 or 1 index element from the tuple, as True equals 1, and False equals 0

>>> secure = True
>>> ('http','https')[0]
'http'
>>> ('http','https')[1]
'https'
>>> ('http','https')[secure]
'https'
>>> ('http','https')[False]
'http'

However, a cleaner way of doing this would be :

protocol = "http" if request.is_secure() else "https"

This is a clever ternary operator in python. Based on the boolean result it will pick one of those two strings.

If False (0) will pick the first one and if True (1) the second one.

Look it like this:

>>>('http://', 'https://')[False]
'http://'

>>>('http://', 'https://')[True]
'https://'

It can also be achieved like this:

protocol = 'https://' if request.is_secure() else 'http://' 

protocols = ('http://', 'https://')

This creates a two-item tuple of the two possible protocols

secure = request.is_secure()

This returns True or False, equivalent to 0 or 1

protocols[secure]

This picks the correct element that matches the security

request.is_secure() will evaluate to True if the connection is secure (HTTPS: HTTP over TLS) or False if non-secure (standard HTTP).

So, if request.is_secure() is True, then:

protocol = ('http://', 'https://')[request.is_secure()]
# Will resolve as:
protocol = ('http://', 'https://')[True]
# Which is:
protocol = ('http://', 'https://')[1]
# And results in.
protocol == 'https://'

Or, if request.is_secure() is False, then:

protocol = ('http://', 'https://')[request.is_secure()]
# Will resolve as:
protocol = ('http://', 'https://')[False]
# Which is:
protocol = ('http://', 'https://')[0]
# And results in.
protocol == 'http://'

• NOTE: The boolean constants True and False resolve to the integers 1 and 0 respectively because bool is a sub-class of int.

The purpose of this is to determine what HTTP scheme (secure or non-secure) to use for links.

request.is_secure() returns either True or False. Thus if it's True, it selects the item in index 1 from the list (True equals 1), else it selects the item in index 0 from the list.

Thus, http and https point to not secure and secure respectively.