Pythonic ways to use 'else' in a for loop

I have hardly ever noticed a python program that uses else in a for loop.

I recently used it to perform an action based on the loop variable condition while exiting; as it is in the scope.

What is the pythonic way to use an else in a for loop? Are there any notable use cases?

And, yea. I dislike using break statement. I'd rather set the looping condition complex. Would I be able to get any benefit out of it, if I don't like to use break statement anyway.

Worth noting that for loop has an else since the language inception, the first ever version.

What could be more pythonic than PyPy?

Look at what I discovered starting at line 284 in ctypes_configure/configure.py:

    for i in range(0, info['size'] - csize + 1, info['align']):
        if layout[i:i+csize] == [None] * csize:
            layout_addfield(layout, i, ctype, '_alignment')
            break
    else:
        raise AssertionError("unenforceable alignment %d" % (
            info['align'],))

And here, from line 425 in pypy/annotation/annrpython.py (clicky)

if cell.is_constant():
    return Constant(cell.const)
else:
    for v in known_variables:
        if self.bindings[v] is cell:
            return v
    else:
        raise CannotSimplify

In pypy/annotation/binaryop.py, starting at line 751:

def is_((pbc1, pbc2)):
    thistype = pairtype(SomePBC, SomePBC)
    s = super(thistype, pair(pbc1, pbc2)).is_()
    if not s.is_constant():
        if not pbc1.can_be_None or not pbc2.can_be_None:
            for desc in pbc1.descriptions:
                if desc in pbc2.descriptions:
                    break
            else:
                s.const = False    # no common desc in the two sets
    return s

A non-one-liner in pypy/annotation/classdef.py, starting at line 176:

def add_source_for_attribute(self, attr, source):
    """Adds information about a constant source for an attribute.
    """
    for cdef in self.getmro():
        if attr in cdef.attrs:
            # the Attribute() exists already for this class (or a parent)
            attrdef = cdef.attrs[attr]
            s_prev_value = attrdef.s_value
            attrdef.add_constant_source(self, source)
            # we should reflow from all the reader's position,
            # but as an optimization we try to see if the attribute
            # has really been generalized
            if attrdef.s_value != s_prev_value:
                attrdef.mutated(cdef) # reflow from all read positions
            return
    else:
        # remember the source in self.attr_sources
        sources = self.attr_sources.setdefault(attr, [])
        sources.append(source)
        # register the source in any Attribute found in subclasses,
        # to restore invariant (III)
        # NB. add_constant_source() may discover new subdefs but the
        #     right thing will happen to them because self.attr_sources
        #     was already updated
        if not source.instance_level:
            for subdef in self.getallsubdefs():
                if attr in subdef.attrs:
                    attrdef = subdef.attrs[attr]
                    s_prev_value = attrdef.s_value
                    attrdef.add_constant_source(self, source)
                    if attrdef.s_value != s_prev_value:
                        attrdef.mutated(subdef) # reflow from all read positions

Later in the same file, starting at line 307, an example with an illuminating comment:

def generalize_attr(self, attr, s_value=None):
    # if the attribute exists in a superclass, generalize there,
    # as imposed by invariant (I)
    for clsdef in self.getmro():
        if attr in clsdef.attrs:
            clsdef._generalize_attr(attr, s_value)
            break
    else:
        self._generalize_attr(attr, s_value)