KeyError even though key exist

Question

It is very strange, even though I can see that the key exist it still gives me an error:

import numpy as np
stim_end_time = 4000
bin_times = np.arange(0,stim_end_time+100,0.025)
time_to_fr = {bin_times[i]:0 for i in range(len(bin_times[:-1]))}
print(0.075 in time_to_fr)
print(0.075 in time_to_fr.keys())
print(np.sort(time_to_fr.keys())[:10])
time_to_fr[0.075]

False
False
[0.    0.025 0.05  0.075 0.1   0.125 0.15  0.175 0.2   0.225]
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-3-d4c6a4c93742> in <module>()
      6 print(0.075 in time_to_fr.keys())
      7 print(np.sort(time_to_fr.keys())[:10])
----> 8 time_to_fr[0.075]

KeyError: 0.075

You are relying on floating point numbers to print exact representations. They do not. Floating point numbers as dictionary keys are fraught with difficulty, especially if you are generating floats. — juanpa.arrivillaga, Sep 22 '18 at 01:22

score 1 · Accepted Answer · answered Sep 22 '18 at 01:09

You need to round the float values:

import numpy as np

stim_end_time = 4000
bin_times = np.arange(0, stim_end_time + 100, 0.025)
time_to_fr = {np.round(bin_times[i], 4) : 0 for i in range(len(bin_times[:-1]))}
print(0.0750 in time_to_fr)
print(0.0750 in time_to_fr.keys())
print(time_to_fr[0.0750])

Output

True
True
0

See this.

KeyError even though key exist

1 Answers1