app.py

from transformers import pipeline
import streamlit as st
import re

unmasker = pipeline('fill-mask', model='distilbert-base-uncased')

def main():
    st.title('EN sentence mask filling')
    st.markdown('Mask a word with [MASK]. For example, **I [MASK] dog for a walk**')
    masked = st.text_input('Masked sentence','Please insert a sentence')
    
    mask_str = '[MASK]'
    mask_check = re.search(masked, mask_str)
    
    if mask_check:
        output = unmasker(masked)
    else:
        print('Sentence is not masked!!!')
  
if __name__ == "__main__":
    main()

x = re.search("^The.*Spain$", txt)