In this lab, you will learn file I/O, JSON files, and CSV files in Python. Packages you will need are:

• os
• csv
• json

Part 1: File I/O

Reading and writing text files is typically very straightforward. Here is an overview of file I/O in Python.

1. Getting input filename from command line file_in = input(Enter name of input file: )

1. Checking if file exists and manipulating pathnames if path.isfile(os.path.join(os.getcwd(),file_in))

c. Open/Close and modifying file position

Another way of opening the file is to use with statement. The use of with statement establishes a context in which the file will be used and when control leaves the with block, the file will be closed automatically. You dont need to use the with statement, but if you dont use it, make sure you remember to close the file. with open(file_in,r+) as f:

print (f.tell())

d. Read/Write to Files

There are several ways of reading and writing to files in Python. Here we show some of them.

One way of reading the file is: read_data = f.read() An alternate way of reading line by line by iterating over the file is: for line in f: print(line)

In order to write to a file,

f.writelines(Yay! Written to file on Friday, 9/9/16 😀
)

Part 2: JSON

JSON file format is used to save generic data programmatic data structures as strings and is commonly used for serialization. JSON is good for storing simple data structures into text file and sending data to other people.

zipCodes = [60290,60601,60602,60603,60604,60605,60606]

# dump into a file f = open(example2.json,w) json.dump(zipCodes,f)

f.close()

# load back into Python f = open(example2.json,r) zipCodes2 = json.load(f)

f.close()

# compare

print(Checking zipcodes) print(zipCodes == zipCodes2)

Part 3: JSON / read

In this example, we will download a JSON file from a URL and display the file one line at a time.

print(Downloading JSON file and printing entire file:) response = get(http://data.cs1656.org/hours.json) print(response.content)

print(Loading as JSON and iterating one line at a time:) hours = json.loads(response.content) print(hours)

print(
Iterating over JSON:) for line in hours: print (line)

Part 4: Convert to CSV On your own

For the next task you need to write a python program to convert the JSON file (downloaded from Part 4) into a CSV file that you need to save to disk. To do this you should look up the csv module and the writer() function in particular.

Part 5: Read CSV On your own

For the next task you need to write a python program to read the CSV file from disk and display its raw contents (without recognizing rows or fields).

Part 6: Read from CSV / rows On your own

For the next task you need to write a python program to read the CSV file from disk and display its contents one row at a time (without recognizing fields).

Part 7: Read from CSV / cells On your own

For the next task you need to write a python program to read the CSV file from disk and display its contents one row at a time and then, within each row, one field at a time