I leverage a number of different programming and scripting tools. Recently, I found myself in a situation where I had to write code to loop through a range of dates to do some operations, by month, in not one, not two…but three different languages: Scala, Python, and Bash. The coding principles are the same across the technologies, but the syntax sure is different.

Here are code examples in four technologies–I threw in PowerShell for good measure–for looping through a range of dates. I loop by month, but these could easily be adapted to loop by day or year or whatever increment fits your needs.

Scala

import java.time.LocalDate
import java.time.format.DateTimeFormatter
import java.util.Date

val start = LocalDate.of(2020, 1, 1) // inclusive in loop
val end = LocalDate.of(2020, 9, 1) // excluded from loop

val template = "This loop is for Year %1$d and Month (zero padded) %2$s \n"

val date_range = Iterator.iterate(start) { _.plusMonths(1) }.takeWhile(_.isBefore(end))
while(date_range.hasNext){
	val d = date_range.next
	val s = template.format(d.getYear, d.format(DateTimeFormatter.ofPattern("MM")))
	print(s)
}

Python

import datetime
import calendar

start = datetime.date(2020, 1, 1)
end = datetime.date(2020, 9, 1)
template = "This loop is for Year {0} and Month (zero padded) {1:%m}"

while start != end:
	s = template.format(start.year, start)
	print(s)
	days_in_month = calendar.monthrange(start.year, start.month)[1]
	start = start + datetime.timedelta(days=days_in_month)

Bash

start=2020-1-1
end=2020-9-1

while [ "$start" != "$end" ]; do
	s="`date -d "$start" +"This loop is for Year %Y and Month (zero padded) %m"`"
	echo s
	start=$(date -I -d "$start + 1 month")
done

PowerShell

$start = get-date "2020-1-1"
$end = Get-Date "2020-9-1"

while($start -ne $end){
    "This loop is for Year {0:yyyy} and Month (zero padded) {0:MM}" -f $start
    $start = $start.AddMonths(1)
}