Simple If Statement doesn't work

[Jack_Sparrow]

Hi guys,
I have this column:

Start Time
0 2017-05-29 18:36:27
1 2017-06-12 19:00:33
2 2017-02-13 17:02:02
3 2017-04-24 18:39:45
4 2017-01-26 15:36:07

I want to calculate the Most Frequent Months of Travel.
There are my steps:

#transform strart date into datetime
df['Start Time'] = pd.to_datetime(df['Start Time'])
#generate new column with months
df['month'] = df['Start Time'].dt.month
#calculate the Frequent Months of Travel
popular_month = df['month'].mode()[0]
#rename int into str
df1['month_name']:
    if popular_month = 1:
        return 'January'
    elif popular_month = 6:
        return 'June'
    else:
        return 'Others'
print('\nThe Most Frequent Months of Travel:', month_name)

I have a problem with rename month as an int (1, 2, 3, etc.) into str (January, February etc.)

What is the right if statement here?

Thank you!