# dict comprehension
new_d = {key: value for key, value in d.iteritems() if key >= guard_condition }

# resize while iterating
for key in d:
    if key < guard_condition:
        del d[key]

In [140]: d = {item: item for item in xrange(10000)};

In [142]: guard_condition = 9000;

In [144]: %timeit new_d = {key: value for key, value in d.iteritems() if key >=
100 loops, best of 3: 2.54 ms per loop

In [140]: d = {item: item for item in xrange(10000)};

In [149]: def del_iter(d, guard_condition):
   .....:     for key in d.keys():
   .....:         if key < guard_condition:
   .....:             del d[key]
   .....:

In [150]: %timeit del_iter(d, guard_condition)
1000 loops, best of 3: 232 us per loop

import cProfile, pstats, StringIO
pr = cProfile.Profile()
pr.enable()

guard_condition = int(raw_input("Enter guard_condition: "))

d = {item: item for item in xrange(10000000)};

new_d = {key: value for key, value in d.iteritems() if key >= guard_condition }

def del_iter(d, guard_condition):
    for key in d.keys():
        if key < guard_condition:
            del d[key]

del_iter(d, guard_condition)

pr.disable()
s = StringIO.StringIO()
sortby = 'cumulative'
ps = pstats.Stats(pr, stream=s).sort_stats(sortby)
ps.print_stats()
print s.getvalue()

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     1    2.794    2.794    2.794    2.794 {raw_input}
     1    1.263    1.263    1.263    1.263 dictDel1.py:7(<dictcomp>)
     1    1.030    1.030    1.030    1.030 dictDel1.py:9(<dictcomp>) <-- dict comprehension
     1    0.892    0.892    0.976    0.976 dictDel1.py:11(del_iter) <-- resize while iterating
     1    0.085    0.085    0.085    0.085 {method 'keys' of 'dict' objects}
     1    0.000    0.000    0.000    0.000 {method 'iteritems' of 'dict' objects}
     1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}

ncalls  tottime  percall  cumtime  percall filename:lineno(function)
     1    3.316    3.316    3.316    3.316 {raw_input}
     1    1.247    1.247    1.247    1.247 dictDel1.py:7(<dictcomp>)
     1    0.937    0.937    1.052    1.052 dictDel1.py:11(del_iter) <-- resize while iterating
     1    0.787    0.787    0.787    0.787 dictDel1.py:9(<dictcomp>) <-- dict comprehension
     1    0.115    0.115    0.115    0.115 {method 'keys' of 'dict' objects}
     1    0.000    0.000    0.000    0.000 {method 'iteritems' of 'dict' objects}
     1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}