**'Super Pi Day'**(3-14-15).

Not in my date system!

**ISO-8601**is a formal standard for the only sane way to write dates and times.

Today is

**2015-03-14**.

Right now, it's

**2015-03-14T11:37:01**.

The ordinal date is

**2015-073**.

This week is

**2015-W11**.

They're general to specific, which just makes sense.

When these dates are used in file names and other strings, alphanumeric sorting automatically orders them in time (at least for the next eight millennia... then the standard will need to be updated to a default five digits for the year!).

UPDATE: Neil deGrasse Tyson agrees:

### When Is Pi Day?

Fortunately, a Python list comprehension will tell us when the REAL Super Pi Day occurs.

**p = list(str(N(pi,digits=100)/10))[2:]**

pidays = [''.join(p[:i]+['-']+p[i:i+2]+['-']+p[i+2:i+4]) for i in range(0,len(p)-4) if(p[:i]!=[] and 0<int(''.join(p[i:i+2]))<=12 and 0<int(''.join(p[i+2:i+4]))<=31)]

show(pidays)

pidays = [''.join(p[:i]+['-']+p[i:i+2]+['-']+p[i+2:i+4]) for i in range(0,len(p)-4) if(p[:i]!=[] and 0<int(''.join(p[i:i+2]))<=12 and 0<int(''.join(p[i+2:i+4]))<=31)]

show(pidays)

In the first 1000 digits of pi, there are 41 Pi Days.

In the first 100 digits of pi, only one Pi Day appears:

31415926535897932384626433832795028841971693993751058209749445923078164-06-28

See you on June 28th in 3*10^70 years!

(note:

**the universe is only 10^10 years old**)

### Non-Calendar Pi Days

How about ordinal Pi Days?

**numdigits=100**

p = list(str(N(pi,digits=numdigits)/10))[2:]

pidays = [''.join(p[:i]+['-']+p[i:i+3]) for i in range(0,len(p)-4) if(p[:i]!=[] and 0<int(''.join(p[i:i+3]))<=365)]

show(pidays[0:5])

print "There are " + str(len(pidays)) + " ordinal Pi Days in the first " + str(numdigits) + " digits of pi"

p = list(str(N(pi,digits=numdigits)/10))[2:]

pidays = [''.join(p[:i]+['-']+p[i:i+3]) for i in range(0,len(p)-4) if(p[:i]!=[] and 0<int(''.join(p[i:i+3]))<=365)]

show(pidays[0:5])

print "There are " + str(len(pidays)) + " ordinal Pi Days in the first " + str(numdigits) + " digits of pi"

There are 34 ordinal Pi Days in the first 100 digits of Pi (which makes sense!).

We missed

**3-141**(Year 3, May 21) and

**314-159**(Year 314, June 08), but the next ordinal pi day is just around the corner on

**314159265-358**(Year 314159265, December 24th).

And week date Pi Days?

**numdigits=100**

p = list(str(N(pi,digits=numdigits)/10))[2:]

pidays = [''.join(p[:i]+['-W']+p[i:i+2]+['-']+p[i+2:i+3]) for i in range(0,len(p)-4) if(p[:i]!=[] and 0<int(''.join(p[i:i+2]))<=52 and 0<int(''.join(p[i+2:i+3]))<=7)]

show(pidays[0:5])

print "There are " + str(len(pidays)) + " week date Pi Days in the first " + str(numdigits) + " digits of pi"

p = list(str(N(pi,digits=numdigits)/10))[2:]

pidays = [''.join(p[:i]+['-W']+p[i:i+2]+['-']+p[i+2:i+3]) for i in range(0,len(p)-4) if(p[:i]!=[] and 0<int(''.join(p[i:i+2]))<=52 and 0<int(''.join(p[i+2:i+3]))<=7)]

show(pidays[0:5])

print "There are " + str(len(pidays)) + " week date Pi Days in the first " + str(numdigits) + " digits of pi"

**0003-W14-1**(0003-03-30)

**0031-W41-5**(0031-10-09)

**314159-W26-5**(314159-06-??)

Of course,

**pi is the wrong number to get excited about anyway**.

### When Is Tau Day?

**τ,**

**the more natural choice for a constant**than pi.

next calendar date:

**62831853-07-17**

Much sooner than calendar pi day.

next ordinal date:

6283-185 (6283-07-04)U-S-A! U-S-A!

next week date:

6283-W18-5 (6283-05-05)

A busy year for tau fans!

### When Is e Day?

Ah, Euler's Number—the base of the natural logarithm.

Calendar date:

**27182818284590452353602874713526624977572470936999595749669676277240766303535475945713821785251664274274663919320-03-05**

It's 10^42 times further off than the next calendar pi day!

Ordinal date:

**2718-281**(2718-10-08)

Practically tomorrow!

Week date:

**2718-W28-1**(2718-07-08)

Of the dates determined, this is the closest of all.

List comprehensions! Learn some Python and automate all kinds of tedious string manipulations. The

**Python documentation**is good and there are all kinds of

**free interactive online Python textbooks**out there.

**Sage Math Cloud**is a great place to play without installing anything—I did the manipulations above in

**this Sage Math worksheet**.