将函数打印输出分配给字符串变量

Question

I have the below function that loops through two lists and prints out a selection of vegetables and then fruits.

def Selection():
    print("VEGETABLES FOR THE WEEK:\n")
    for veg in veg_selection:
        print(veg.upper())
    print("\n")
    print("FRUITS FOR THE WEEK:\n")
    for fruit in fruit_selection:
        print(fruit.upper())

So the result could look like:

VEGETABLES FOR THE WEEK:

BROCOLLI
PEAS
CARROTS
SWEET CORN
WHITE ONIONS


FRUITS FOR THE WEEK:

GRAPEFRUIT
CHERRIES
ORANGE
COCONUT
RASPBERRIES

I'm struggling to get my head around assigning the printed results of the function to a single variable that contains the formatted string. Would I need to save the results as a text file and then read it in again? Can I just use text concatenation? I'm unsure how to deal with the for loops in the function? Any help really appreciated.

Answer 1

One of solutions would be to store all itermediate strings to container and join them afterwards. Quoting docs:

string.join(words[, sep]) Concatenate a list or tuple of words with intervening occurrences of sep. The default value for sep is a single space character. It is always true that string.join(string.split(s, sep), sep) equals s.

So sample code would look like:

import os

def selection():
    strings = []
    strings.append("VEGETABLES FOR THE WEEK:\n")
    for veg in veg_selection:
        strings.append(veg.upper())
    strings.append("\n")
    strings.append("FRUITS FOR THE WEEK:\n")
    for fruit in fruit_selection:
        strings.append(fruit.upper())
    return os.linesep.join(strings)

s = selection()  # s now contains output string, and nothing is printed
print(s)  # print whole string at once

os.linesep is cross-os constant with correct newline character.

The string used to separate (or, rather, terminate) lines on the current platform. This may be a single character, such as '\\n' for POSIX, or multiple characters, for example, '\\r\\n' for Windows. Do not use os.linesep as a line terminator when writing files opened in text mode (the default); use a single '\\n' instead, on all platforms.

Also, semi-related question: Good way to append to a string .

Answer 2

Probably the simplest way to do it is to just add an extra step appending the text to your variable wherever you need to. See below:

def Selection():
    output_text = "VEGETABLES FOR THE WEEK:\n"
    print("VEGETABLES FOR THE WEEK:\n")
    for veg in veg_selection:
        output_text += veg
        print(veg.upper())
    output_text += "\n"
    print("\n")
    output_text += "FRUITS FOR THE WEEK"
    print("FRUITS FOR THE WEEK:\n")
    for fruit in fruit_selection:
        output_text += fruit
        print(fruit.upper())

You could change your code to output the output_text string at the end instead of printing each line too.

Answer 3

You can just concatenate to a single string variable like so:

def Selection():
    output = "VEGETABLES FOR THE WEEK:\n"
    for veg in veg_selection:
        output += veg.upper() + "\n"
    output += "\nFRUITS FOR THE WEEK:\n"
    for fruit in fruit_selection:
        output += fruit.upper() + "\n"

You can then either print the string straight away by adding to the end:

print(output)

or return the string for use elsewhere by adding at the end:

return output

Answer 4

Turn your function into generator:

def Selection():
    yield "VEGETABLES FOR THE WEEK:\n"
    for veg in veg_selection:
        yield veg.upper()
    yield "\n"
    yield "FRUITS FOR THE WEEK:\n"
    for fruit in fruit_selection:
        yield fruit.upper()

Then, turning into a string is trivial:

'\n'.join(Selection())

To print the result:

for line in Selection():
    print(line)