TypeError：字符串索引必须是整数，而不是Python字典上的str

Question

I'm stuck, on what I'm sure is something simple, but I'm just going around in circles now. The following code is a snippet of a script that iterates over some values I've entered into lists and dictionaries and produces text files that I can feed into another program. The problem I'm having is when attempting to loop round the Direction list and have corresponding values from the relevant dictionary print to file I get the following error:

TypeError: string indices must be integers, not str

Direction = ('E', 'NE')

E = {
    'InitialHeading': 0,
    'InitialX': 22.480,
    'InitialY': 0.000,
    'ActiveCurrent': '10y_Current_W'}

NE = {
    'InitialHeading': 45,
    'InitialX': 15.896,
    'InitialY': 15.896,
    'ActiveCurrent': '10y_Current_SW'}

casenumber = 0

for Offset in Direction:

            # CREATE INDIVIDUAL TEXT FILES
            casenumber = casenumber + 1
            filename = 'Case%.3d.txt' % casenumber
            f = open(filename, 'w')
            print >>f, 'InitialHeading: ', Offset['InitialHeading']
            print >>f, 'InitialX: ', Offset['InitialX']
            print >>f, 'InitialY: ', Offset['InitialY']
            print >>f, 'ActiveCurrent: ', Offset['ActiveCurrent']
            f.close()

If I replace Offset with the name of the dictionary so the line reads as follows:

print >>f, 'InitialHeading: ', E['InitialHeading']

Then the output is exactly what I want and I know that Offset is equal to E when I run the file, as I added a line to print the value of Offset to the console window.

Why doesn't it recognise the dictionary name when it's the same value as the variable Offset , which is obtained from the Direction list? This piece of code is from nested for loops, so I need to be able to refer to the lists & dictionaries to obtain the values, rather than a more manual alternative.

Answer 1

You are using subscription syntax on the Offset variable, which is a string , taken from Direction .

You cannot use the string in Offset as a placeholder for the variable with the same name directly. Instead, *store the dictionary:

E = {
    'InitialHeading': 0,
    'InitialX': 22.480,
    'InitialY': 0.000,
    'ActiveCurrent': '10y_Current_W'}

NE = {
    'InitialHeading': 45,
    'InitialX': 15.896,
    'InitialY': 15.896,
    'ActiveCurrent': '10y_Current_SW'}

Direction = (E, NE)

or better still, use another dictionary to wrap the directions:

Direction = {
    'E': {
        'InitialHeading': 0,
        'InitialX': 22.480,
        'InitialY': 0.000,
        'ActiveCurrent': '10y_Current_W'},

    'NE': {
        'InitialHeading': 45,
        'InitialX': 15.896,
        'InitialY': 15.896,
        'ActiveCurrent': '10y_Current_SW'}
}

Now you can loop over that dictionary and have both a string name for the direction and the settings associated with it:

for direction, settings in Directions.items():
    # CREATE INDIVIDUAL TEXT FILES
    casenumber = casenumber + 1
    filename = 'Case%.3d.txt' % casenumber
    with open(filename, 'w') as f:
        print >>f, 'InitialHeading: ', settings['InitialHeading']
        print >>f, 'InitialX: ', settings['InitialX']
        print >>f, 'InitialY: ', settings['InitialY']
        print >>f, 'ActiveCurrent: ', settings['ActiveCurrent']