PDA_note_week3.py

"""
Python Data Analysis
WEEK THREE

Course Note and Quiz 
"""

# CSV = Comma-separated values
SPLIT = "====================================="

"""
Example code to read and parse a CSV file.
"""

def parse(csvfilename):
    """
    Reads CSV file named csvfilename, parses
    it's content and returns the data within
    the file as a list of lists.
    """
    table = []
    with open(csvfilename, "r") as csvfile:
        for line in csvfile:
            line = line.rstrip()
            columns = line.split(',') # this returns a list
            table.append(columns)
    return table


def print_table(table):
    """
    Print out table, which must be a list
    of lists, in a nicely formatted way.
    """
    for row in table:
        # Header column left justified
        print("{:<19}".format(row[0]), end='')
        # Remaining columns right justified
        for col in row[1:]:
            print("{:>4}".format(col), end='')
        print("", end='\n')

table = parse("hightemp.csv")
print_table(table)

print("")
print("")

# not so nicely formatted 
table2 = parse("hightemp2.csv")
print_table(table2)


"""
Using the csv module.
"""
print(SPLIT)

import csv

def parse(csvfilename):
    """
    Reads CSV file named csvfilename, parses
    it's content and returns the data within
    the file as a list of lists.
    """
    table = []
    with open(csvfilename, "r") as csvfile:
        csvreader = csv.reader(csvfile,
                               skipinitialspace=True)
        for row in csvreader:
            table.append(row)
    return table


def print_table(table):
    """
    Print out table, which must be a list
    of lists, in a nicely formatted way.
    """
    for row in table:
        # Header column left justified
        print("{:<19}".format(row[0]), end='')
        # Remaining columns right justified
        for col in row[1:]:
            print("{:>4}".format(col), end='')
        print("", end='\n')

table = parse("hightemp.csv")
print_table(table)

print("")
print("")

table2 = parse("hightemp2.csv")
print_table(table2)


"""
Using csv.DictReader.
"""
print(SPLIT)

import csv

MONTHS = ('Jan', 'Feb', 'Mar', 'Apr',
          'May', 'Jun', 'Jul', 'Aug',
          'Sep', 'Oct', 'Nov', 'Dec')

def dictparse(csvfilename, keyfield):
    """
    Reads CSV file named csvfilename, parses
    it's content and returns the data within
    the file as a dictionary of dictionaries.
    """
    table = {}
    with open(csvfilename, "rt", newline='') as csvfile:
        csvreader = csv.DictReader(csvfile,
                                   skipinitialspace=True)
        for row in csvreader:
            table[row[keyfield]] = row
    return table


def print_table(table):
    """
    Print out table, which must be a dictionary
    of dictionaries, in a nicely formatted way.
    """
    print("City               ", end='')
    for month in MONTHS:
        print("{:>6}".format(month), end='')
    print("")
    for name, row in table.items():
        # Header column left justified
        print("{:<19}".format(name), end='')
        # Remaining columns right justified
        for month in MONTHS:
            print("{:>6}".format(row[month]), end='')
        print("", end='\n')

table = dictparse("hightemp.csv", 'City')
print_table(table)

"""
CSV reader options.
"""
print(SPLIT)

def dictparse(csvfilename, keyfield, separator, quote, quotestrategy):
    """
    Reads CSV file named csvfilename, parses
    it's content and returns the data within
    the file as a dictionary of dictionaries.
    """
    table = {}
    with open(csvfilename, "rt", newline='') as csvfile:
        csvreader = csv.DictReader(csvfile,
                                   skipinitialspace=True,
                                   delimiter=separator, # default ,
                                   quotechar=quote, # default "
                                   quoting=quotestrategy)
        for row in csvreader:
            table[row[keyfield]] = row
    return table, csvreader.fieldnames


def print_table(table, fieldnames):
    """
    Print out table, which must be a dictionary
    of dictionaries, in a nicely formatted way.
    """
    print("{:<19}".format(fieldnames[0]), end='')
    for field in fieldnames[1:]:
        print("{:>6}".format(field), end='')
    print("")
    for name, row in table.items():
        # Header column left justified
        print("{:<19}".format(name), end='')
        # Remaining columns right justified
        for field in fieldnames[1:]:
            print("{:>6}".format(row[field]), end='')
        print("", end='\n')

# csv.QUOTE_MINIMAL only use "" when it's absolutely neccessary 
table, fieldnames = dictparse("hightemp.csv", 'City', ',', '"', csv.QUOTE_MINIMAL)

print(fieldnames)
print_table(table, fieldnames)

print("")
print("")

# csv.QUOTE_NONNUMERIC every item that is not numeric must be quoted 
table2, fieldnames2 = dictparse("hightemp2.csv", 'City', ',', '"', csv.QUOTE_NONNUMERIC)
print_table(table2, fieldnames2)

print("")
print("")

table3, fieldnames3 = dictparse("hightemp3.csv", 'City', ' ', "'", csv.QUOTE_NONNUMERIC)
print_table(table3, fieldnames3)


"""
Examples code for experimenting with options to the csv.read() and csv.write() methods
"""
print(SPLIT)

# Function that prints 2D table to console

def print_table(table):
    """
    Echo a nested list to the console
    """
    for row in table:
        print(row)


# Options for reading a CSV file

def read_csv_file(file_name, file_delimeter):
    """
    Given a CSV file path and a delimiter as strings,
    read the data into a 2D table and return the table
    """
       
    with open(file_name, newline='') as csv_file:       # don't need to explicitly close the file now
        csv_table = []
        csv_reader = csv.reader(csv_file, delimiter=file_delimeter)
        for row in csv_reader:
            csv_table.append(row)
    return csv_table


def csv_delimiter_examples():
    """
    Run some example of reading CSV files using different delimiter options
    """
    number_table = read_csv_file("number_table.csv", " ")
    print_table(number_table)
    print()
    name_table = read_csv_file("name_table.csv", ",")
    print_table(name_table)



csv_delimiter_examples()

print(SPLIT)
# Options for writing a CSV file

def write_csv_file(csv_table, file_name, file_delimiter, quoting_value):
    """
    Given a nested list csv_table, write the data into a
    CSV file with the name file_name
    """
    
    with open(file_name, 'w', newline='') as csv_file:
        csv_writer = csv.writer(csv_file, delimiter=file_delimiter, quoting=quoting_value)
        for row in csv_table:
            csv_writer.writerow(row)
            
def csv_quoting_examples():
    """
    Run some example of writing 2D tables as CSV files using various quoting options
    """
    name_table = read_csv_file("name_table.csv", ",")
    name_table.append([1, 2, 3])
    write_csv_file(name_table, "name_table_minimal.csv", ",", csv.QUOTE_MINIMAL)
    write_csv_file(name_table, "name_table_all.csv", ",", csv.QUOTE_ALL)
    write_csv_file(name_table, "name_table_nonnumeric.csv", ",", csv.QUOTE_NONNUMERIC)
    #write_csv_file(name_table, "name_table_none.csv", ",", csv.QUOTE_NONE)        # no escapechar is set for lots of quotes

   
#csv_quoting_examples()