Port Old Python to python 3 expression help

[RaymondSeth_III1]

I am trying to port this code to python 3 and am having a terrible time trying to recreate this expression. I am really new to python but more specifically these expressions. the varible dateStart and dateEnd are int as well as Num in the table being a LONG

expression = "mid(trim(str([Num])), 5, 4) not between '" + dateStart + "' and '" + dateEnd + "'"

arcpy.management.SelectLayerByAttribute("workLyr", "NEW_SELECTION", expression)

[LeanneRodriguez]

So mid(string, 5, 4) meaning give me the substring beginning at character 5 and 4 chars long, right?

In python it would be:

str(!FieldName!)[5:8]

or.. give me a string starting at position 5 and ending at position 8
so it returns characters at positions 5,6,7,8 

[RaymondSeth_III1]

That may help with part of it, but I am not sure I am formatting the entire expression correctly as I keep getting invalid expression error. The quotes and single quotes are really confusing.

[JoshuaBixby]

Python slicing is start to stop, not start through stop, so [5:8] returns only 3 characters and not 4 characters.

[Kara_Shindle]

Is the expression variable correct?  You set the expression with the variable named "expression1" but the function is taking a variable named "expression"

[RaymondSeth_III1]

yes sorry that was a copy and paste error as it appears a couple of times in the code but it matches in the code.

[RaymondSeth_III1]

So, I have changed it to this and still get an invalid expression error. 

expression = "str(!Num!)[4:7] not between '" + dateStart + "' and '" + dateEnd + "'"

arcpy.management.SelectLayerByAttribute("workLyr", "NEW_SELECTION", expression)

[JoshuaBixby]

When I try just building your expression I get an error before I even get to the arcpy tool:  (The specific values I used don't matter for test building expression, just the data types matter, and I had to change !Num! to just Num for testing)

>>> Num = 123456
>>> dateStart = 1
>>> dateEnd = 2
>>> expression = "str(Num)[4:7] not between '" + dateStart + "' and '" + dateEnd + "'"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can only concatenate str (not "int") to str
>>>

Are you sure you are pasting your exact code?

[RaymondSeth_III1]

This was the original code. 

expression = "mid(trim(str([Num])), 5, 4) not between '" + dateStart + "' and '" + dateEnd + "'"

arcpy.management.SelectLayerByAttribute("workLyr", "NEW_SELECTION", expression)

[JoshuaBixby]

If you are using ArcGIS Pro, I suggest you use literal strings or f-strings:

expression = f"{str(Num)[4:7]} not between {dateStart} and {dateEnd}"