Question

I would like to convert specific ascii file to csv.
This ascii file has own specification and I post below relevant fragments.

line A starts with code 66TP:

66TP        1003    54.437269600149717.012388003107655.5139691177756                :10.008677993245250.01231534739191

line B starts with C6NM:

C6NM0821.565823793411260.900167346000671.2812114953994820.81007696688170033                                1679475490.0000000001679475527.0000000001

As you see above individual values are not separated but their differentiation is
by position and length in line.

spec of line A:

1 Position   Length Data format Description of field

2   1           2   Type code   Record type code = 66
3   3           2   Derivation  Derivation code
4   5           16  Name        Point name
5   21          16  Latitude    Latitude
6   37          16  Longitude   Longitude
7   53          16  Distance    WGS84 ellipsoidal height at APC
8   69          16  Text 16     Feature code
9   85          1   GPS Method  Measurement method
10  86          1   Classification  Classification of the point
11  87          16  Distance    Horizontal precision
12  103         16  Distance    Vertical precision

spec of line B:

1   Position Length Data format Description of field
2   1           2   Type code   Record type code = C6
3   3           2   Derivation  Derivation code
4   5           2   Integer 2   Minimum number of satellites
5   7           1   Boolean     Relative DOPs
6   8               16  Scalar  PDOP (maximum)
7   24          16  Scalar  HDOP (maximum)
8   40          16  Scalar  VDOP (maximum)
9   56          16  Scalar  RMS
10  72          4   Integer 4   Number of GPS positions used
11  76          16  Distance    Horizontal standard deviation
12  92          16  Distance    Vertical standard deviation
13  108         4   Integer 4   Start GPS week
14  112         16  Scalar  Start GPS time in seconds to 3dp
15  128         4   Integer 4   End GPS Week
16  132         16  Scalar  End GPS time in seconds to 3dp
17  148         1   Monitor Status

my desired output is to merge both lines and would be like:

1003,54.4372696001497,17.0123880031076,55.5139691177756,0.009,0.012,8,1.6,0.9,1.28,20.8,033,1679,475490.0,1679,475527.0

and here’s input file where I marked individual values with square brackets:

66TP        [1003]    [54.4372696001497][17.0123880031076][55.5139691177756]                :1[0.00867799324525][0.01231534739191]

C6NM[082][1.56582379341126][0.90016734600067][1.28121149539948][20.81007696688170][033]                                [1679][475490.000000000][1679][475527.0000000001]

Sorry for quite long post but I have no idea how could I describe it in shorter way.
I am an amateur beginner programmer and I’d like to ask you for any hint that let me start
handling such type of data.

Answer 1

Since you know the position of each element on each line, use a string slice to grab each element.

For example,

type_code = linea[0:2]
(derivation, name) = (linea[2:4], linea[4:20])

To take this a step further, you could write a little function to split a line apart given a list of the lengths for the line.

Code

def split_string_by_position(a_string, lengths):
    result = []
    position = 0
    for length in lengths:
        result.append(a_string[position:position+length])
        position = position+length
    return result


line = '66TP        1003    54.437269600149717.012388003107655.5139691177756'
lengths = [2, 2, 16, 16, 16, 16, 16, 16, 1, 1, 16, 16]

print(split_string_by_position(line, lengths))

Output

['66', 'TP', '        1003    ', '54.4372696001497', '17.0123880031076', '55.5139691177756', '', '', '', '', '', '']

This just returns a list of the data elements. You could takes this a step further by providing a variable name along with each length ([[2,'type'], [2,'derivation'],...]) and change the function around a little so it returns a dict instead so you could then access it by using the_result['variable_name']

A few ideas to play with. http://learnpythonthehardway.org/ would be a good thing for you to work through so you learn the basics of the language.