Scope of lambda functions and their parameters?

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When a lambda is created, it doesn’t make a copy of the variables in the enclosing scope that it uses. It maintains a reference to the environment so that it can look up the value of the variable later. There is just one m. It gets assigned to every time through the loop. After the loop, the variable m has value 'mi'. So when you actually run the function you created later, it will look up the value of m in the environment that created it, which will by then have value 'mi'.

One common and idiomatic solution to this problem is to capture the value of m at the time that the lambda is created by using it as the default argument of an optional parameter. You usually use a parameter of the same name so you don’t have to change the body of the code:

for m in ('do', 're', 'mi'):
    funcList.append(lambda m=m: callback(m))

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