如何在 Python 中漂亮地打印 CSV 文件

Question

How can I pretty print a CSV file using Python, not any external tool?

For example I have this CSV file:

title1|title2|title3|title4
datalongdata|datalongdata|data|data

data|data|data|datalongdatadatalongdatadatalongdatadatalongdatadatalongdata
data|data'data|dat

I would like to transform it to visually look like a table. For example, to something like that:

+ --------------------------------------------------------------------------------------------------- +
| title1       | title2       | title3 | title4                                                       |
+ --------------------------------------------------------------------------------------------------- +
| datalongdata | datalongdata | data   | data                                                         |
|              |              |        |                                                              |
| data         | data         | data   | datalongdatadatalongdatadatalongdatadatalongdatadatalongdata |
| data         | data'data    | dat    |                                                              |
+ --------------------------------------------------------------------------------------------------- +

Answer 1

Usage:

pretty.pretty_file( filename , ***options*)

Reads a CSV file and prints visually the data as table to a new file. filename , is the given CSV file. The optional ***options* keyword arguments is the union of Python's Standard Library csv module Dialects and Formatting Parameters and the following list:

• new_delimiter : the new column separator ( default " | ")
• border : boolean value if you want to print the border of the table ( default True)
• border_vertical_left : the left border of the table ( default "| ")
• border_vertical_right : the right border of the table ( default " |")
• border_horizontal : the top and bottom border of the table ( default "-")
• border_corner_tl : the top-left corner of the table ( default "+ ")
• border_corner_tr : the top-right corner of the table ( default " +")
• border_corner_bl : the bottom-left corner of the table ( default same as border_corner_tl )
• border_corner_br : the bottom-right corner of the table ( default same as border_corner_tr )
• header : boolean value if the first row is a table header ( default True)
• border_header_separator : the border between the header and the table ( default same as border_horizontal )
• border_header_left : the left border of the table header ( default same as border_corner_tl )
• border_header_right : the right border of the table header ( default same as border_corner_tr )
• new_filename : the new file's filename ( default "new_" + filename )
• newline : defines how the rows of the table will be separated ( default "\\n")

Example:

import pretty_csv
pretty_csv.pretty_file("test.csv", header=False, border=False, delimiter="|")

Python 3:

This is a Python 2 implementation. For Python 3, you have to change the 2 occurrences of the line open(filename, "rb") as input: to open(filename, "r", newline="") as input: since csv.reader in Python 3 wants the file to be opened in text mode.

Module:

import csv
import os

def pretty_file(filename, **options):
    """
    @summary:
        Reads a CSV file and prints visually the data as table to a new file.
    @param filename:
        is the path to the given CSV file.
    @param **options:
        the union of Python's Standard Library csv module Dialects and Formatting Parameters and the following list:
    @param new_delimiter:
        the new column separator (default " | ")
    @param border:
        boolean value if you want to print the border of the table (default True)
    @param border_vertical_left:
        the left border of the table (default "| ")
    @param border_vertical_right:
        the right border of the table (default " |")
    @param border_horizontal:
        the top and bottom border of the table (default "-")
    @param border_corner_tl:
        the top-left corner of the table (default "+ ")
    @param border_corner_tr:
        the top-right corner of the table (default " +")
    @param border_corner_bl:
        the bottom-left corner of the table (default same as border_corner_tl)
    @param border_corner_br:
        the bottom-right corner of the table (default same as border_corner_tr)
    @param header:
        boolean value if the first row is a table header (default True)
    @param border_header_separator:
        the border between the header and the table (default same as border_horizontal)
    @param border_header_left:
        the left border of the table header (default same as border_corner_tl)
    @param border_header_right:
        the right border of the table header (default same as border_corner_tr)
    @param newline:
        defines how the rows of the table will be separated (default "\n")
    @param new_filename:
        the new file's filename (*default* "/new_" + filename)
    """

    #function specific options
    new_delimiter           = options.pop("new_delimiter", " | ")
    border                  = options.pop("border", True)
    border_vertical_left    = options.pop("border_vertical_left", "| ")
    border_vertical_right   = options.pop("border_vertical_right", " |")
    border_horizontal       = options.pop("border_horizontal", "-")
    border_corner_tl        = options.pop("border_corner_tl", "+ ")
    border_corner_tr        = options.pop("border_corner_tr", " +")
    border_corner_bl        = options.pop("border_corner_bl", border_corner_tl)
    border_corner_br        = options.pop("border_corner_br", border_corner_tr)
    header                  = options.pop("header", True)
    border_header_separator = options.pop("border_header_separator", border_horizontal)
    border_header_left      = options.pop("border_header_left", border_corner_tl)
    border_header_right     = options.pop("border_header_right", border_corner_tr)
    newline                 = options.pop("newline", "\n")

    file_path = filename.split(os.sep)
    old_filename = file_path[-1]
    new_filename            = options.pop("new_filename", "new_" + old_filename)

    column_max_width = {} #key:column number, the max width of each column
    num_rows = 0 #the number of rows

    with open(filename, "rb") as input: #parse the file and determine the width of each column
        reader=csv.reader(input, **options)
        for row in reader:
            num_rows += 1
            for col_number, column in enumerate(row):
                width = len(column)
                try:
                    if width > column_max_width[col_number]:
                        column_max_width[col_number] = width
                except KeyError:
                    column_max_width[col_number] = width

    max_columns = max(column_max_width.keys()) + 1 #the max number of columns (having rows with different number of columns is no problem)

    if max_columns > 1:
        total_length = sum(column_max_width.values()) + len(new_delimiter) * (max_columns - 1)
        left = border_vertical_left if border is True else ""
        right = border_vertical_right if border is True else ""
        left_header = border_header_left if border is True else ""
        right_header = border_header_right if border is True else ""

        with open(filename, "rb") as input:
            reader=csv.reader(input, **options)
            with open(new_filename, "w") as output:
                for row_number, row in enumerate(reader):
                    max_index = len(row) - 1
                    for index in range(max_columns):
                        if index > max_index:
                            row.append(' ' * column_max_width[index]) #append empty columns
                        else:
                            diff = column_max_width[index] - len(row[index])
                            row[index] = row[index] + ' ' * diff #append spaces to fit the max width

                    if row_number==0 and border is True: #draw top border
                        output.write(border_corner_tl + border_horizontal * total_length + border_corner_tr + newline)
                    output.write(left + new_delimiter.join(row) + right + newline) #print the new row
                    if row_number==0 and header is True: #draw header's separator
                        output.write(left_header + border_header_separator * total_length + right_header + newline)
                    if row_number==num_rows-1 and border is True: #draw bottom border
                        output.write(border_corner_bl + border_horizontal * total_length + border_corner_br)

Answer 2

Since this question was asked, a lot has changed. I thought I'd give a newer alternative solution. You mentioned "not any external tool", but I think it's fair to use pip packages. For instance, this is the exact problem that tabulate solves. According to their docs, you could do:

import csv ; from StringIO import StringIO
table = list(csv.reader(StringIO("spam, 42\neggs, 451\n")))
print(tabulate(table))

And get a Markdown user-friendly table. If you have pandas available, it could be even easier:

print(pandas.read_csv(filename).to_markdown(index=False))

And you get something like:

| food   |   amount |
|:-------|---------:|
| apple  |       12 |
| pear   |       34 |