Conditional dictionary explicit initialization

Question

I need to add to the list a dictionary based on the number of elements in a given tuple. The idea is below:

# t is tuple containing 1 or 2 elements, l is list
l = list()
l.append({
 'A': t[0],
 if len(t) > 1: ('B': t[1])
})

So, if t = [7, 8] then l = [{'A': 7, 'B': 8}] and if t = [7] then l = [{'A': 7}].

How can I accomplish this?

• Jblasco: The options are only one or two elements?
• Colin vH: Please reconsider which answer you have accepted. Jblasco's works, but ajcr's is much simpler.

Answer 1

You could just use an if statement.

d = { 'A':t[0] }
if len(t) > 1:
 d['B'] = t[1]
l = [d]

Or you could use a comprehension:

l = [ { chr(ord('A')+i):v for i,v in enumerate(t) } ]

That will work if the length of your tuple is between 0 and 26. (After that you run out of letters.)

Answer 2

Alternatively you could write the following line to create the dictionary:

[dict(zip(['A', 'B'], t))]

Then if t = [7, 8]:

>>> [dict(zip(['A', 'B'], t))]
[{'A': 7, 'B': 8}]

And if t = [7]:

>>> [dict(zip(['A', 'B'], t))]
[{'A': 7}]

The function zip creates tuples from t and the list of letters only up to the length of the shortest list. dict maps the tuples to dictionary keys/values.

Answer 3

Since the zip function stops in the shortest of the two emails, I like the option:

l.append({key:value for key, value in zip(['A', 'B'], t)})

• Colin vH: {key: value for key, value in ...} is equivalent to dict(...).
• kylieCatt: You can also import string and use string.letters.upper()[:26] in the palce of ['A', 'B']. It makes it a little more extensible in case you don't know the length of t.
• Jblasco: You are right, @ColinvH. That's the answer that ajcr posted a minute before I did, while I was writting mine. In all fairness, ajcr should be the chosen "right" answer.

Answer 4

Your conditional expression should be written like so:

l.append({'A': t[0], 'B': t[1]} if len(t) > 1 else {'A': t[0]})

If the tuple has more than one item, then we add {'A': t[0], 'B': t[1]} to the list. Otherwise, we add {'A': t[0]}.

---

Alternately, you could add dict(zip('AB', t)) to the list:

l.append(dict(zip('AB', t)))

this will work in either case:

>>> t = (1, 2)
>>> dict(zip('AB', t))
{'A': 1, 'B': 2}
>>> t = (1,)
>>> dict(zip('AB', t))
{'A': 1}
>>>