The complexity of this function doen't change before it was:

for char in result: # line 50
    for replace in replaceMap: # line 53
        compare(replace, char)

and now it's

for replace in replaceMap: # line 47
    for char in result: # line 48
        compare(replace, char)

But I found a better way of doing it, with regex

In D15896#338474, @ognarb wrote:

The complexity of this function doen't change before it was:

for char in result: # line 50
    for replace in replaceMap: # line 53
        compare(replace, char)

and now it's

for replace in replaceMap: # line 47
    for char in result: # line 48
        compare(replace, char)

But I found a better way of doing it, with regex

Don't forget that line 53 is a QMap::find, based on a red-black tree, which implies that not all the comparisons will be carried out.

Also, depending on the iteration order, your second solution could have modified the semantics of the function (~ -> $\\sim$ -> \\$\\sim\\$).

Now, I'm not sure about the regexp solution. It relies on heavy machinery, and it still requires two passes over toConv. Furthermore, some comments would be needed to explain what is being replaced.

I guess we would need some benchmarks to determine which one is faster...

My suggestion would still be to simplify the original code a little bit ;)