While not "A" , unless "AB"

Question

While parsing an ASCII file, I want to perform some operations on a section of lines.

The length of the section will vary, so I made a while loop that should continue until I reach a line starting with "A", indicating that the section has ended. However, within the section there will be some lines starting with "AB", which I want to include.

So I'm looking for something like: while not line[0] == "A", unless line[:2] == "AB"

I.e. "AA", "AC", "A$" or "A-whatever" should break the loop, but "AB" should not.

I'm a novice and haven't found the right search terms for a nice clean solution to this, though I'm sure one must exist, or do I need to resort to regex?

Edit: As requested here is a sample:

*SIGNAL* $$$1 2 -2 ; 
R1.2                            U1.36                           
3.1    3.635  0 0.3048 1792  THERMAL 
14.92  14     65 0.3048 1792  THERMAL 

*SIGNAL* $$$2 2 -2 ; 
R1.1                            U1.40                           
3.1    2.365  0 0.3048 1792  THERMAL 
18.984 14     65 0.3048 1792  THERMAL 

*SIGNAL* $$$3 2 -2 ; 
U1.16                           U1.22                           
24.064 26.7   0 0.3048 1792  THERMAL 
18     29.2   1 0.3048 1280 STANDARDVIA THERMAL  TEARDROP N 90 90 
17.968 29.168 1 0.3048 1536 
17.968 26.7   65 0.3048 768  THERMAL  TEARDROP P 90 90 
U1.16                           R3.2                            
24.064 26.7   1 0.3048 1280  THERMAL  TEARDROP N 90 90 
29     26.7   1 0.3048 1536 
29.7   26     1 0.3048 1536 
33.4   26     1 0.3048 1536 
33.4   26.035 65 0.3048 768  THERMAL  TEARDROP P 90 90 
U1.22                           U1.2                            
17.968 26.7   0 0.3048 1792  THERMAL 
21.016 14     65 0.3048 1792  THERMAL 
U1.26                           U1.22                           
13.142 24.922 0 0.3048 1792  THERMAL 
17.968 26.7   65 0.3048 1792  THERMAL 
R2.2                            U1.2                            
17     3.65   0 0.3048 1792  THERMAL 
21.016 14     65 0.3048 1792  THERMAL 

*SIGNAL* $$$4 2 -2 ; 
R2.1                            U1.4                            
17     2.35   0 0.3048 1792  THERMAL 
23.048 14     65 0.3048 1792  THERMAL 

*SIGNAL* $$$5 2 -2 ; 
R3.1                            U1.6                            
33.4   24.765 0 0.3048 1792  THERMAL 
25.842 15.778 65 0.3048 1792  THERMAL 

*TESTPOINT*
...

In this case, the next section is called "TESTPOINT", but that will vary. The only known character is the beginning "*", so unfortunately that includes all the "SIGNAL"-lines as well.

Answer 1

This would be perfect for a regular expression.

For example,

^A(?!B).*

will match a line that starts with A and does not have a B afterwards.

You could probably match entire sections this way, for example (assuming that you want to match everything from Z to A (unless AB), then

(?s)^Z.*?^A(?!B)

would match that. If you can specify your problem more precisely, it's possible to design a more specific regex.

Answer 2

You may want to use "or"

while line[0] != "A" or line[:2] == "AB":
    # your code here