webinar-python-file-writing-2022-02-12

# Working with Files - Reading and Writing
# Sat Feb 12

# opening a file
# older syntax
# f = open("test.txt", "r") # r, w, a, and r+, w+, a+... don't worry about those
# # work with the file
# f.close()

# newer way, the with/open() block
with open("test.txt", "r") as f: # r is default mode, but I'll include
    # work with file
    # 2 ways I normally grab the contents of file
    # read() # returns the entire contents of the file, as one big string
    # readlines() # returns a list of strings, kinda like str.split()
    myList = f.readlines()

# when you leave the block, the file is closed
# in read mode, you might as well close as soon as possible to save memory
# I still have myList
print(myList)

for line in myList:# line here is a str in the list
    # print(type(line))
    # print("Is string?", isinstance(line, str))
    # line = line.rstrip() # strip()
    print(line, end="-") # print(end="\n")
    # if I want update the list
    # myList[x]
    myList[myList.index(line)] = line.rstrip()
print()
print(myList)

print("---------------")
# we could use the csv module and its csv.reader() instead
import csv
# with open("mock_data.csv", "r") as cFile:
#     myList = cFile.readlines()
#
# print(myList)
# for line in myList:
#     # line = line.rstrip()
#     row = line.rstrip().split(",")
#     print(row[3])
with open("mock_data.csv", "r") as cFile:
    myVar = csv.reader(cFile, delimiter=",")
    myVar = list(myVar) # I like to recast a csv.reader file as a list...

print(myVar) # Look! It's a LIST of LISTS

# with open()...
# write() # in "w" mode, destructive; in "a" mode it appends to end

# Let's look at the first part of  Lab 29.1
filename = input().rstrip()
# open in read
with open(filename, "r") as f:
    # myList = f.readlines()
    myList = [line.rstrip() for line in f.readlines()]
# print(myList) # looks good!
tvDict = {}
# for item in myList: # but range() would be better to get index
for i in range(0, len(myList), 2):
    key = myList[i]
    # value = myList[i+1]

    if key in tvDict:  # if it's ALREADY in there
        tvDict[key] += "; {}".format(myList[i + 1])
    else:
        tvDict[key] = myList[i + 1]  # so this is the normal thing to do...
print(tvDict)

# write output_keys.txt
with open("output_keys.txt", "w") as f:
    for k in tvDict:
        # print("{}: {}\n".format(k, tvDict[k])) # writing looks the same...
        f.write("{}: {}\n".format(k, tvDict[k])) # it's just strings!
# That's MOST of writing out the output_keys.txt file they asked for, but...
# In unit testing you will get a curve ball: you have to control for
# "zero padded" numbers vs not: "07" vs "7" in your keys


# if you're ever reading and writing in the same open() block...
f.seek() # moves to position in filestream you're reading/writing, like a scrubber