Inno Setup: Determining the data directory at install time

Ryan Ginstrom — Wed, 08 Apr 2009 12:28:14 +0000

Inno Setup is a fantastic and free application for creating Windows setup programs. It takes so much of the hassle out of the process that it's almost fun.

I recently needed to extend Inno Setup with a custom code section: I needed to install the program's data to the Common App Data folder or the Local App Data folder, depending on a selection made during the installation process (install for all users, or just me). Here's the script I came up with:

; AppDataTest.iss
[Setup]
AppName=AppData Test
AppVerName=AppData Test 0.1
DefaultDirName={pf}\AppDataTest
DefaultGroupName=AppDataTest
OutputDir=Setup

[Files]
Source: AppDataTest.iss; DestDir: {app}\;
Source: AppDataTest.iss; DestDir: {code:DefAppDataFolder}\Test\;

[Tasks]
Name: common; Description: "&All users"; GroupDescription: "Install For:"; Flags: exclusive unchecked
Name: local; Description: "Just &me"; GroupDescription: "Install For:"; Flags: exclusive

[Icons]
Name: {group}\Uninstall AppDataTest; Filename: {uninstallexe}

[Code]
function DefAppDataFolder(Param: String): String;
begin
if IsTaskSelected('common') then
Result := ExpandConstant('{commonappdata}')
else
Result := ExpandConstant('{localappdata}')
end;

I created a radio button for the [Tasks] page, asking whether the user wants to install the application for all users, or just herself.

Then in the [Code] section, I created a function to expand "DefAppDataFolder" to commonappdata or localappdata, depending on whether "common" or "local" is selected in in the [Tasks] section (IsTaskSelected('common')).

This value is then expanded in the [Files] section, at this line:

Source: AppDataTest.iss; DestDir: {code:DefAppDataFolder}\Test\;

Here's the setup script (AppDataTest.iss), and the resulting setup program (setup.exe).

Iterating over a window in Python

Ryan Ginstrom — Sun, 07 Dec 2008 05:36:37 +0000

This weekend, I had a fairly common problem: given a sequence of elements and an element in that sequence, I needed to get the next element; if the element was the last in the sequence, then I needed the first element.

My first stab at a solution was pretty straightforward:

def item_after(elements, item):
for i in range(len(elements)):
if elements[i] == item:
try:
return elements[i+1]
except IndexError:
return elements[0]

This works for the intended purpose, although the C-style looping doesn't sit too well with me. But this code has a major flaw: it doesn't work for generators.

After a little more thought, I decided that what I wanted was to iterate over a window of two items in the sequence, and if the first item matched, return the second one.

from itertools import chain

def by_pairs(iterable):
sequence = iter(iterable)
previous = sequence.next()
while True:
current = sequence.next()
yield previous, current
previous = current

To illustrate how this works:

>>> for pair in by_pairs(range(6)):
print pair

(0, 1)
(1, 2)
(2, 3)
(3, 4)
(4, 5)

The new item_after function:

def item_after2(elements, item):
pairs = by_pairs(elements)
first, second = pairs.next()
for a, b in chain([(first, second)], pairs):
if a == item:
return b
return first

In the new item_after function, I peel off the first pair so I can cache the first element, then glob it back on the front of the sequence using itertools.chain.

After a little more thought, I realized that the by_pairs function can be made generic to handle a window of any size.

from collections import deque

def window_iter(elements, n):
sequence = iter(elements)
window = deque()
while True:
element = sequence.next()
window.append(element)
if len(window) == n:
yield window
window.popleft()

The item_after function now looks like this:

def item_after3(elements, item):
pairs = window_iter(elements, 2)
first, second = pairs.next()
for a, b in chain([(first, second)], pairs):
if a == item:
return b
return first

And with a little data: one of my pets gets a treat every day. I know who got the treat yesterday; who gets it next?

pets = [pet for pet in "Bear Lady Mikey Jerry Kiri".split()]
print "Pet after Kiri is", item_after3(pets, "Kiri")
print "Pet after Lady is", item_after3(pets, "Lady")

The output:

Pet after Kiri is Bear
Pet after Lady is Mikey

I can think of a lot of potential uses for this window iterator. One is in natural language processing, when calculating the "stickiness" of words in a corpus. You could iterate over a window of three words, calculating the collocations of words before and after the middle word.

Here's a rather contrived example: calculating the average temperature on days when the previous two days were 80 degrees or higher.

def ave_temp_after(temp, temps):
after_temps = [z for x, y, z in window_iter(temps, 3)
if x > temp < y]
return sum(after_temps) / float(len(after_temps))

tempdata = "99 101 85 91 71 64 67 90 81 101".split()
temps = (float(x) for x in tempdata)
temp = ave_temp_after(80, temps)

print "Average temperature after two days of 80+:", temp

Output:

Average temperature after two days of 80+: 87.0

It strikes me that this would be great for those baseball statistics guys:

This is just the third time since 1963 that a left-handed pinch hitter has broken a bat on three consecutive Wednesdays.

I'm waiting for a call from The Show any day now.

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Inno Setup: Determining the data directory at install time

Iterating over a window in Python