[reportlab-users] Looks like a bug ...

Johan Paul Glutting reportlab-users@reportlab.com
Mon, 04 Oct 2004 10:37:44 +0200

I think I found a bug in ReportLab. When drawing a Line Chart (I am 
using the HorizontalLineChart class), if the first value in a series is 
Null, the labels on the points are shifted to the right, although the 
lines are drawn correctly. Example:

data = [None, 10, 15, 20]

produces something like this (flat line  - this is ASCII graphics after 
all ...)

          None           10                15
x         x_________x_________x

where this data prints out like this:

data = [10, 15, 20, None]

10               15            20
x__________x_______x           x

The first set of data can be fixed by substituting "0" for "None", like 

data = [0, 10, 15, 20]

0                10              15              20

I discovered this because I am doing data on student registration, by 
degree. Some degrees just did not exist before a certain date, and so 
the number of students is Null, rather than zero, and there should be no 
line drawn on the graph at all...

Some fake code that should reproduce this:

D = Drawing()
lc1 =  HorizontalLineChart()
lc2 =  HorizontalLineChart()
lc1.data =  [[None, 10, 15, 20],[None, 30, 35, 40]]
lc2.data =  [[0, 10, 15, 20],[0, 30, 35, 40]]
lc1.lines.symbol = makeMarker('FilledDiamond')
lc2.lines.symbol = makeMarker('FilledDiamond')
lc1.lineLabelFormat = '%s'
lc2.lineLabelFormat = '%s'

I will take a look at the code and see if I can figure out what is going 
on (it looks like the data drawing funciton is taking al the values, but 
the label drawing function starts the label list from the first value 
onto the first visible data point, instead of the proper index...).



JP Glutting
Oficina de Qualitat		Plaša VÝctor Siurana, 1
Universitat de Lleida		25003 Lleida
Tel: 973 703 103		Fax: 973 702 036