Python scripting in ABAQUS

I have a python script to create ABAQUS model and run a job.

I want to create a loop over a variable

index=1:1:4,

create four different models and run the four jobs for each model.

A model is named 'Model-1' for instance in the following line:

##-----------------------------------------------------------------------
mdb.models['Model-1'].ConstrainedSketch(name='__profile__', sheetSize=sqrlen) 
##-----------------------------------------------------------------------

In creating a loop, I create a string as follows: 

##-----------------------------------------------------------------------
index='1'
modelname='\''+'Model' + index+ '\'' 

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mdb.models[modelname].ConstrainedSketch(name='__profile__', sheetSize=sqrlen)
##------------------------------------------------------------------------- 

When I run the script in ABAQUS, it gives error saying 'Model1'as follows:

##------------------------------------------------------------------------- 

  File "d:/abaqus_working_directory/scripting_example/simulation/scripting_loop.py", line 22, in <module>
    mdb.models[modelname].ConstrainedSketch(name='__profile__', sheetSize=sqrlen)  #### sqrlen
KeyError: 'Model1'
Exit from main file  [Kernel]: d:/abaqus_working_directory/scripting_example/simulation/scripting_loop.py
##------------------------------------------------------------------------- 

I want to use the string modelname( with value ='Model-1') instead of writing 'Model-1' in the python script

mdb.models['Model-1'].ConstrainedSketch(name=....)
mdb.models[modelname].ConstrainedSketch(name=...)

when it is called.

Any help is deeply appreciated.

Sincerely, Me.