Consider this example:

```
#! /usr/bin/env python
import ROOT
dictio = {}
N = 3
for ind in range(0, N):
key = ROOT.TString("key_{}".format(ind))
H = ROOT.TH1F(key.Data(), "h", 4, 0.0, 3.0)
r = ROOT.TRandom(0)
H.FillRandom("gaus", r.Integer(600))
dictio[key] = H
print "key %s id %s integral %f" % (key, hex(id(dictio[key])), H.Integral())
print "*****"
for key in dictio:
print "key %s id %s integral %f" % (key, hex(id(dictio[key])), H.Integral())
```

The output is:

```
key key_0 id 0x7f2da76fa530 integral 228.000000
key key_1 id 0x7f2da76fa830 integral 116.000000
key key_2 id 0x7f2da76fa8f0 integral 7.000000
*****
key key_2 id 0x7f2da76fa8f0 integral 7.000000
key key_0 id 0x7f2da76fa530 integral 7.000000
key key_1 id 0x7f2da76fa830 integral 7.000000
```

Why is the integral of all histograms in the dictionary equal to the integral of the last histogram inserted?

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