在Python中，如何在通过循环创建的python列表中获取条目的值

Question

I am writing Python code to pull data from a csv file and format it into geoJSON. I want to also grab single entries from the data to include in the properties of the geoJSON. For example, I convert a column of csv timestamps into geoJSON, and I also want to pull out the first and last timestamps in that list for the properties below:

   "properties": {
        "species": "racoon",
        "id": "12345",
        "first transmitted": "Aug 12, 2014",
        "last transmitted": "Nov 1, 2015"
}

I have written Python code that converts a column of timestamps from the csv to the geoJSON format:

# loop through the csv by row skipping the first
iter = 0

timevals = ""
for row in rawData:
    iter += 1
    if iter >= 2 and itemid == row[1]:
        rawtime = row[4]
        rawtime = rawtime.replace("T", " ")
        rawtime = rawtime.replace("Z", "")
        timevals += template_time % int( time.mktime(time.strptime(rawtime, '%Y-%m-%d %H:%M:%S') ))

This gives me the list of timestamps from the csv file formatted for my geoJSON file. Now I want to grab the first and last timestamp in that list. I altered it like this in order to try to grab the first:

# loop through the csv by row skipping the first
iter = 0

timevals = ""
for row in rawData:
    iter += 1
    if iter >= 2 and itemid == row[1]:
        rawtime = row[4]
        rawtime = rawtime.replace("T", " ")
        rawtime = rawtime.replace("Z", "")
        timeval = int( time.mktime(time.strptime(rawtime, '%Y-%m-%d %H:%M:%S') ))
        timevals += template_time % timeval
    startTime = timeval.iloc[0]
    print startTime

My error is:

startTime = timeval.iloc[0]
AttributeError: 'int' object has no attribute 'iloc'

What is the way to write this?

EDIT I got the startTime by initializing

startTime = ""

and then writing

if startTime == "":
    startTime = rawtime

so now I have the following, plus the endTime:

# loop through the csv by row skipping the first
iter = 0
startTime = ""

for row in rawData:
    iter += 1
    if iter >= 2 and itemid == row[1]:  # itemid
        rawtime = row[4]
        rawtime = rawtime.replace("T", " ")
        rawtime = rawtime.replace("Z", "")

        if startTime == "":
            startTime = rawtime

        endTime = rawtime

This ends up producing the first and final values, startTime and endTime, though its a bit of a trick and I was wondering if there was something more pythonic.

Answer 1

Thanks for the clarification edit. Can you easily hold the data in memory? If so, you have a simple path: define a function for the conversion, then apply that only to the first and last items.

I'm assuming that you're skipping the first line because it's header information. If so, then you don't really need to check for it explicitly; its 2nd entry won't match itemid, anyway.

def convert_time(rawtime):
    rawtime = row[4]
    rawtime = rawtime.replace("T", " ")
    rawtime = rawtime.replace("Z", "")

row_stream = [row in rawData if row[1] == itemid]
startTime = convert_time(row_stream[0])
endTime = convert_time(row_stream[-1])

If you have too much data for this to work, then trade the list comprehension for a generator, and let the Python run-time take care of the optimizations:

row_stream = (row in rawData if row[1] == itemid)