Pandas: access fields within field in a DataFrame
Multi-indexing might be helpful. See this.
But the below was the immediate solution that came to mind. I think it's a little more elegant than what you came up with (fewer obscure numbers, more interpretable natural language):
import pandas as pd
df = pd.read_json('test_file.json')
df = df.append(df) # just to give us an extra row to loop through below
df.reset_index(inplace=True) # not really important except to distinguish your rows
for _ , row in df.iterrows():
    currNumbDict = len(row['analytics'])
    print(currNumbDict)