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I thought you were going to get the separate postal codes data and use that?
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The separate postal codes aren't the one common people use here.
The postal codes we use are the ones stored in alternate_names which means that the column for postal codes become useless for France.
It's easy enough to extract just the postcode from the alternate_names field, for France.
It looks like the postcode always pre-ceeds any text and it's always 5 digits long.
There's a few ways you could extract the code easily.
Read off the first 5 chars from' alternate_name's and use a regular expression to match it against the postcode format. The regular expression is even given in the country_info data.
After some research, the codes in admin4 are in fact INSEE codes.
The real postal codes that everyone use in their daily lives are stored in alternate_names.
For example, the postal code for Creteil is 94000 but admin4 is set to 94028 which is the INSEE code.