How to convert a string to a number if it has commas in it as thousands separators?

import locale
locale.setlocale( locale.LC_ALL, 'en_US.UTF-8' ) 
locale.atoi('1,000,000')
# 1000000
locale.atof('1,000,000.53')
# 1000000.53

There are several ways to parse numbers with thousands separators. And I doubt that the way described by @unutbu is the best in all cases. That's why I list other ways too.

1. The proper place to call setlocale() is in __main__ module. It's global setting and will affect the whole program and even C extensions (although note that LC_NUMERIC setting is not set at system level, but is emulated by Python). Read caveats in documentation and think twice before going this way. It's probably OK in single application, but never use it in libraries for wide audience. Probably you shoud avoid requesting locale with some particular charset encoding, since it might not be available on some systems.

2. Use one of third party libraries for internationalization. For example PyICU allows using any available locale wihtout affecting the whole process (and even parsing numbers with particular thousands separators without using locales):

   NumberFormat.createInstance(Locale('en_US')).parse("1,000,000").getLong()

3. Write your own parsing function, if you don't what to install third party libraries to do it "right way". It can be as simple as int(data.replace(',', '')) when strict validation is not needed.

Replace the commas with empty strings, and turn the resulting string into an int or a float.

>>> a = '1,000,000'
>>> int(a.replace(',' , ''))
1000000
>>> float(a.replace(',' , ''))
1000000.0