Python, what is this for loop doing?

Question

I have scoured the internet and I cannot find any reference to this type of for loop:

variable = [(item["attribute1"], item["attribute2]") for item in piece_of_json_data]

I am using this to update wtform's SelecField choices:

form.SelectField.choices = variable

but I can only get it to work if I replace one of the attributes in parenthesis with a static number:

variable = [(1, item["attribute2"]) for item in piece_of_json_data]

but that sets the value of the option field to "1", when I need the option values to be one of the attributes as a string.

Does this create a dict? a tuple? is there some kind of terminology for this that I can use to find documentation?

This line `variable = [1, item["attribute2]) for item in piece_of_json_data]` has a syntax error, it won't run And the first line creates a list of tuples. — Devesh Kumar Singh, May 27 '19 at 06:01
https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions — Devesh Kumar Singh, May 27 '19 at 06:03
Ok so I am using list comprehension to create tuple. All of the examples use numbers, I can't use a string for the first value? — JSum, May 27 '19 at 06:08

JSum · Accepted Answer · 2019-05-27T06:41:55.700

0

Thanks to the comments, I now understand that I am using list comprehension to create a tuple. The tuple works fine with both string and integer values. My issue has to do with .choices not accepting a string.

I found that my only problem is that I had coerce set to int on my selectfield, so naturally it wanted an integer.

edited May 27 '19 at 06:41

answered May 27 '19 at 06:29

JSum

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Python, what is this for loop doing?

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