feat(peak): adds --func optional argument

Filter the peak memory usage by function. This doesn't isolate the
contribution of the function by itself, but it screens out noise
from setting up the test so an accurate result can be obtained
by mprof peak if the test is otherwise well isolated.

Example usage:

mprof peak --func some.function

The function name is the fully qualified python import name.
You can also figure it out by grepping the dat file for FUNC
entries.

Author: william-silversmith

mprof.py

@@ -835,19 +835,47 @@ def xlim_type(value):
     else:
         pl.show()
 
+def filter_mprofile_mem_usage_by_function(prof, func):
+    if func is None:
+        return prof["mem_usage"]
+
+    if func not in prof["func_timestamp"]:
+        raise ValueError(str(func) + " was not found.")
+
+    time_ranges = prof["func_timestamp"][func]
+    filtered_memory = []
+    
+    # The check here could be improved, but it's done in this
+    # inefficient way to make sure we don't miss overlapping
+    # ranges.
+    for mib, ts in zip(prof["mem_usage"], prof["timestamp"]):
+        for rng in time_ranges:
+            if rng[0] <= ts <= rng[1]:
+                filtered_memory.append(mib)
+
+    return filtered_memory
+
 def peak_action():
     desc = """Prints the peak memory used in data file `file.dat` generated
 using `mprof run`. If no .dat file is given, it will take the most recent
 such file in the current directory."""
     parser = ArgumentParser(usage="mprof peak [options] [file.dat]", description=desc)
     parser.add_argument("profiles", nargs="*",
                     help="profiles made by mprof run")
+    parser.add_argument("--func", dest="func", default=None,
+                        help="""Show the peak for this function. Does not support child processes.""")
     args = parser.parse_args()
     filenames = get_profiles(args)
 
     for filename in filenames:
         prof = read_mprofile_file(filename)
-        print("{}\t{:.3f} MiB".format(prof["filename"], max(prof["mem_usage"])))
+        try:
+            mem_usage = filter_mprofile_mem_usage_by_function(prof, args.func)
+        except ValueError:
+            print("{}\tNaN MiB".format(prof["filename"]))
+            continue
+
+        print("{}\t{:.3f} MiB".format(prof["filename"], max(mem_usage)))
         for child, values in prof["children"].items():
             child_peak = max([ mem_ts[0] for mem_ts in values ])
             print("  Child {}\t\t\t{:.3f} MiB".format(child, child_peak))