import pandas as pd
df = pd.DataFrame({'D': [1, 2, 3, 4]})
df2 = pd.DataFrame({'D': [5, 6, 7, 8]})
df3 = pd.concat([df, df2], ignore_index=True)
print(df3)
# D
#0 1
#1 2
#2 3
#3 4
#4 5
#5 6
#6 7
#7 8
import pandas as pd
df = pd.DataFrame({'D': ['A', 'B', 'C', 'd']})
df
df['D'] = "'" + df['D'] + "'"
print(df)
import pandas as pd
df = pd.DataFrame({'D': ['A', 'B', 'C', 'd']})
df.update("'" + df['D']+ "'")