Programming Forums > Script Programming > Python

Mjordan2nd · Oct 22nd, 2005, 11:40 AM

I decided to learn Python finally. I decided to play around and give myself a challenge to create a spiral, since it would get me used to working with lists and the basic concepts of python. I'm using the Quick Python Book, which says you can use nested lists to create a matrix, which is wha I tried. I wanted to create a 2-dimensional list which is initialized to 1. I tried to do:

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m = [[1]*square]*square]

This worked in creating the nested list, but was ineffective since it seems that each of the nested lists were simply a reference to the same list. I got around it, and did get my spiral function working, but I was wondering if there's a more effective way to initialize seperate lists to 1 value than what I did it. I'm sure the book will show me eventually, I'm just not too far in it yet. Here's what I had.

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>>> def spiral(square):
	m = []
	i = 0
	while i < square:
		m.append([])
		i = i + 1
	del i
	i = 0
	while i<square:
		j = 0
		while j<square:
			m[i].append(1)
			j = j+1
		i = i+1
	del j
	del i
	r = 0
	c = 0
	d = 1
	value = square * square
	while value > 1:
		m[r][c] = value
		if d == 1:
			if c == square-1 or m[r][c+1] !=1:
				d = d + 1
				continue
			else:
				c = c + 1
				value = value - 1
		elif d == 2:
			if r == square-1 or m[r+1][c] !=1:
				d = d + 1
				continue
			else:
				r = r + 1
				value = value - 1
		elif d == 3:
			if c == 0 or m[r][c-1] !=1:
				d = d + 1
				continue
			else:
				c = c - 1
				value = value - 1
		elif d == 4:
			if r == 0 or m[r-1][c] !=1:
				d = 1
				continue
			else:
				r = r - 1
				value = value - 1
	r = 0
	c = 0
	while r<square:
		while c<square:
			print "%3d" % (m[r][c]),
			c = c+1
		c = 0
		r = r+1
		print

This is how I created and initialized the list:

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 m = []
 	i = 0
 	while i < square:
 		m.append([])
 		i = i + 1
 	del i
 	i = 0
 	while i<square:
 		j = 0
 		while j<square:
 			m[i].append(1)
 			j = j+1
 		i = i+1

Thanks in advance for any help.

Arevos · Oct 22nd, 2005, 3:19 PM

You can use list comprehensions:

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[[1 for i in range(square)] for i in range(square)]

Or this will probably work, too:

(Toggle Plain Text)

[[1] * square for i in range(square)]

As an extra point, if you want to loop over a piece of code n times, its usually better to use a for-loop, rather than a while-loop:

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for i in range(n):
   <code>

Mjordan2nd · Oct 22nd, 2005, 3:41 PM

Gotcha. Thanks. I would have used for loops, just haven't learned about loops yet. I just looked at some sample code, and the while-loop seemed more straightforward than the for-loop. I guess I'll skip forward to that chapter and check out how they work. Thanks again.

Oct 22nd, 2005, 11:40 AM	#1
Mjordan2nd The Supreme Ruler Join Date: May 2004 Location: Houston Posts: 1,476 Rep Power: 6	Nested Lists I decided to learn Python finally. I decided to play around and give myself a challenge to create a spiral, since it would get me used to working with lists and the basic concepts of python. I'm using the Quick Python Book, which says you can use nested lists to create a matrix, which is wha I tried. I wanted to create a 2-dimensional list which is initialized to 1. I tried to do: (Toggle Plain Text) m = [[1]square]square] m = [[1]square]square] This worked in creating the nested list, but was ineffective since it seems that each of the nested lists were simply a reference to the same list. I got around it, and did get my spiral function working, but I was wondering if there's a more effective way to initialize seperate lists to 1 value than what I did it. I'm sure the book will show me eventually, I'm just not too far in it yet. Here's what I had. (Toggle Plain Text) >>> def spiral(square): m = [] i = 0 while i < square: m.append([]) i = i + 1 del i i = 0 while i<square: j = 0 while j<square: m[i].append(1) j = j+1 i = i+1 del j del i r = 0 c = 0 d = 1 value = square * square while value > 1: m[r][c] = value if d == 1: if c == square-1 or m[r][c+1] !=1: d = d + 1 continue else: c = c + 1 value = value - 1 elif d == 2: if r == square-1 or m[r+1][c] !=1: d = d + 1 continue else: r = r + 1 value = value - 1 elif d == 3: if c == 0 or m[r][c-1] !=1: d = d + 1 continue else: c = c - 1 value = value - 1 elif d == 4: if r == 0 or m[r-1][c] !=1: d = 1 continue else: r = r - 1 value = value - 1 r = 0 c = 0 while r<square: while c<square: print "%3d" % (m[r][c]), c = c+1 c = 0 r = r+1 print >>> def spiral(square): m = [] i = 0 while i < square: m.append([]) i = i + 1 del i i = 0 while i<square: j = 0 while j<square: m[i].append(1) j = j+1 i = i+1 del j del i r = 0 c = 0 d = 1 value = square * square while value > 1: m[r][c] = value if d == 1: if c == square-1 or m[r][c+1] !=1: d = d + 1 continue else: c = c + 1 value = value - 1 elif d == 2: if r == square-1 or m[r+1][c] !=1: d = d + 1 continue else: r = r + 1 value = value - 1 elif d == 3: if c == 0 or m[r][c-1] !=1: d = d + 1 continue else: c = c - 1 value = value - 1 elif d == 4: if r == 0 or m[r-1][c] !=1: d = 1 continue else: r = r - 1 value = value - 1 r = 0 c = 0 while r<square: while c<square: print "%3d" % (m[r][c]), c = c+1 c = 0 r = r+1 print This is how I created and initialized the list: (Toggle Plain Text) m = [] i = 0 while i < square: m.append([]) i = i + 1 del i i = 0 while i<square: j = 0 while j<square: m[i].append(1) j = j+1 i = i+1 m = [] i = 0 while i < square: m.append([]) i = i + 1 del i i = 0 while i<square: j = 0 while j<square: m[i].append(1) j = j+1 i = i+1 Thanks in advance for any help. __________________ "Every gun that is made, every warship launched, every rocket signifies, in the final sense, a theft from those who hunger and are not fed, from those who are cold and are not clothed. The world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children." - Dwight D. Eisenhower

Oct 22nd, 2005, 3:19 PM	#2
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 4	You can use list comprehensions: (Toggle Plain Text) [[1 for i in range(square)] for i in range(square)] [[1 for i in range(square)] for i in range(square)] Or this will probably work, too: (Toggle Plain Text) [[1] * square for i in range(square)] [[1] * square for i in range(square)] As an extra point, if you want to loop over a piece of code n times, its usually better to use a for-loop, rather than a while-loop: (Toggle Plain Text) for i in range(n): <code> for i in range(n): <code> Last edited by Arevos; Oct 22nd, 2005 at 3:33 PM.

Oct 22nd, 2005, 3:41 PM	#3
Mjordan2nd The Supreme Ruler Join Date: May 2004 Location: Houston Posts: 1,476 Rep Power: 6	Gotcha. Thanks. I would have used for loops, just haven't learned about loops yet. I just looked at some sample code, and the while-loop seemed more straightforward than the for-loop. I guess I'll skip forward to that chapter and check out how they work. Thanks again. __________________ "Every gun that is made, every warship launched, every rocket signifies, in the final sense, a theft from those who hunger and are not fed, from those who are cold and are not clothed. The world in arms is not spending money alone. It is spending the sweat of its laborers, the genius of its scientists, the hopes of its children." - Dwight D. Eisenhower

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Programming Forums > Script Programming > Python

Nested Lists