Cs 151 dictionary writer

Computer Science 151
An introduction to the art of computing
Dictionary Writer
Rudy Martinez

CS151 Spring 2019
File Output
Normal file output:
import csv
writefile = open(‘filename’,’w’,newline=’’) #newline needed if on windows
writer = csv.writer(writefile)
# DATA holds all the records from a dictionary or list
for row in DATA:
writer.writerow(DATA[row]) # this works for both Dictionary but not list
why?
# or
writer.writerows(DATA) # for a dictionary this doesn’t work!!!!

CS151 Spring 2019
Peculiarities of writing lists and dictionaries
List
for row in DATALIST:
writer.writerow(row)
Dictionary
for key in DATADICT.keys():
writer.writerow([key,DATADICT[key]
])
● Remember our last class what was said about for row in DATALIST:
○ For a list a whole row is returned
● Dictionaries are access differently because they are Key:Value pairs.
○ We must create a list of keys to iterate over DATADICT.keys() ← returns list of keys
○ Then we call the DATADICT[key] and we get the Value of that key
● For lists this works well we get a well formed written file.
● For dictionaries we get a key and whatever the Value pair is returned as.
○ In homework 2b we have a list [TMax, TMin]
○ File looks like this: 1994, [77, 47]

CS151 Spring 2019
csv.DictWriter
● DictWriter is a function of the CSV library that knows how to handle Dictionary
objects and can easily write them.
● There is a bit of a catch however …
import csv
writefile = open(‘filename’,’w’,newline=’’) #newline needed if on windows
writer = csv.DictWriter(writefile, fieldnames=[‘date’,’Tmax’,’Tmin’)
writer.writeheader() # Creates header of fieldnames
# Pattern is key:value
writer.writerow({DATADICT[key][0), DATADICT[key][1),DATADICT[key][2)})
Output:
1994 77.15 47.6

CS151 Spring 2019
What’s the difference
writer.writerow([key,DATADICT[key]])
Output:
1994, [77.5, 47.6]
Date as string, List of ints.
writer.writerow({DATADICT[key][0),
DATADICT[key][1),
DATADICT[key][2)})
Output:
1994, 77.5, 47.6
All values as a csv of strings.

CS151 Spring 2019
Dictionary Representation
writer.writerow({DATADICT[key][0), DATADICT[key][1), DATADICT[key][2)})
DATADICT.Keys() Index 0 Index 1 Index 2
Row 0 1994 1994 77.15 47.6

CS151 Spring 2019
Row 0 1994 1994 77.15 47.6
Row 1 1994 1994 74.76 42.15

CS151 Spring 2019
Row 0 1994 1994 77.15 47.6
Row 1 1995 1995 74.76 42.15
Row 2 1996 1996 73.38 44.25

CS151 Spring 2019
Program 2b Rubric 50pts possible
1. Create a file (homework2b.py). 5
2. Your program should open the homework2.csv data file. 5
3. Read the file into a list. You should convert the date to a datetime object,
and you should convert the TMIN and TMAX to integers or float number types.
10
4. You will create a yearly average for TMIN and TMAX. (see pdf for format) 20
5. Create a Dictionary set the key to be the year and the value to be a list containing TMAX, TMIN. 5
6. Write a comma separated value (CSV) file to disk (averagedata.csv) 5

CS151 Spring 2019
Part C Requirements
● Highest temp for each year
○ For each year keep track of the highest temp (max tmax)
● Lowest temp for each year
○ For each year keep track of the lowest temp (min tmin)
● The number of days above average TMAX
○ For each year, if tmax current > avg tmax increment a counter
● The number of day below average TMIN
○ For each year, if tmin current < avg tmin increment a counter
● Write to a csv file,
○ Year, avgTMAX, avgTMIN, High, Low, Days above TMAX, Days below TMIN
○ Write the above file and call it statistics.csv

Cs 151 dictionary writer

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