Error importing BERT: module 'tensorflow._api.v2.train' has no attribute 'Optimizer'
import tensorflow as tf
print(tf.__version__)
!pip uninstall tensorflow==2.2.0
!pip install tensorflow==1.15.0
!pip install bert-tensorflow
try this. it worked for me for the same issue
I tried to use bert-tensorflow in Google Colab, but I got the following error:

--------------------------------------------------------------------------- AttributeError                            Traceback (most recent call
  last)  in ()
        1 import  bert
  ----> 2 from bert import run_classifier_with_tfhub # run_classifier
        3 from bert import optimization
        4 from bert import tokenization
1 frames /usr/local/lib/python3.6/dist-packages/bert/optimization.py
  in ()
       85 
       86 
  ---> 87 class AdamWeightDecayOptimizer(tf.train.Optimizer):
       88   """A basic Adam optimizer that includes "correct" L2 weight decay."""
       89 
AttributeError: module 'tensorflow._api.v2.train' has no attribute
  'Optimizer'

Here is the code I tried:

Install the libraries:

!pip install --upgrade --force-reinstall tensorflow
!pip install --upgrade --force-reinstall tensorflow-gpu
!pip install tensorflow_hub
!pip install sentencepiece
!pip install bert-tensorflow

Run this code:

from sklearn.model_selection import train_test_split
import pandas as pd
from datetime import datetime
from tensorflow.keras import optimizers
import  bert
from bert import run_classifier
from bert import optimization
from bert import tokenization

I've also tried 
import tensorflow.compat.v1 as tf
tf.disable_v2_behavior()
But got the same error.