import pandas as pd
from tqdm import tqdm

df1 = pd.DataFrame({'lkey': 1000*['a', 'b', 'c', 'd'],'lvalue': np.random.randint(0,int(1e8),4000)})
df2 = pd.DataFrame({'rkey': 1000*['a', 'b', 'c', 'd'],'rvalue': np.random.randint(0, int(1e8),4000)})

#this is how you activate the pandas features in tqdm
tqdm.pandas()
#call the progress_apply feature with a dummy lambda 
df1.merge(df2, left_on='lkey', right_on='rkey').progress_apply(lambda x: x)