Falsehoods Programmers Believe

I'm in love with these lists of "Falsehoods Programmers Believe About X." In case you haven't had pleasure, I've collected all the ones I know of here. If I missed any, let me know!

Falsehoods programmers believe about names

• People's names do not change
• People’s names have an order to them
• My system will never have to deal with names from China
• I can safely assume that this dictionary of bad words contains no people’s names in it
• People have names

Falsehoods programmers believe about time

• The time zone in which a program has to run will never change
• The system clock will never be set to a time that is in the distant past or the far future
• One minute on the system clock has exactly the same duration as one minute on any other clock
• A time stamp of sufficient precision can safely be considered unique
• The duration of one minute on the system clock would never be more than an hour

More falsehoods programmers believe about time

• The local time offset (from UTC) will not change during office hours.
• My software is only used internally/locally, so I don’t have to worry about timezones
• I can easily maintain a timezone list myself
• Time passes at the same speed on top of a mountain and at the bottom of a valley

Falsehoods programmers believe about time zones

• Every day without DST changes is 86400 (60 * 60 * 24) seconds long
• If you have two UTC timestamps it is possible to calculate how many seconds will be between them even if one of the timestamps are a year into the future
• The time 23:59:60 is always invalid

Falsehoods programmers believe about geography

• Places have only one official name
• Place names follow the character rules of the language
• Place names can be written with the exhaustive character set of a country
• Places have only one official address
• Street addresses contain street names

Falsehoods programmers believe about addresses

• No buildings are numbered zero
• A road will have a name
• A single postcode will be larger than a single building
• OK, but you don't get multiple postcodes per building
• Addresses will have a reasonable number of characters — less than 100, say

Falsehoods programmers believe about maps

• All coordinates are in “Latitude/Longitude”
• The shortest path between two points is a straight line
• All programmers agree on the ordering of latitude and longitude pairs

Extra Credit:

Update!

Kevin Deldycke has made an even better version of this list, and hosted it on GitHub, where you can make pull requests to add new lists when you find them!