Improves lightgbm conversion speed

[xadupre]

Conversion speed up for lightgbm model. For a big model (~40000 trees), the conversion goes from 3 hours to 10 minutes for lightgbm. Fixes #482.

[lgtm-com]

This pull request introduces 1 alert and fixes 3 when merging ce75d85 into cf660f0 - view on LGTM.com

new alerts:

• 1 for Non-callable called

fixed alerts:

• 3 for Use of the return value of a procedure

[lgtm-com]

This pull request fixes 3 alerts when merging b099fe3 into cf660f0 - view on LGTM.com

fixed alerts:

• 3 for Use of the return value of a procedure

[lgtm-com]

This pull request fixes 3 alerts when merging fe48e76 into cf660f0 - view on LGTM.com

fixed alerts:

• 3 for Use of the return value of a procedure

[lgtm-com]

This pull request fixes 3 alerts when merging 6df0b37 into c1651b1 - view on LGTM.com

fixed alerts:

• 3 for Use of the return value of a procedure

[lgtm-com]

This pull request fixes 3 alerts when merging c97834e into 3d81a0a - view on LGTM.com

fixed alerts:

• 3 for Use of the return value of a procedure

[abhishek9804]

can anyone tell me why i am getting below error on python 3.8, during lightgbm model.
dump_booster_model
ret = json.loads(string_buffer.value.decode('utf-8'), cls=Hook,
TypeError: json_loads_mock() got an unexpected keyword argument 'cls'.