Python 将函数输出写入文件

Question

如果这是一个愚蠢的问题，我很抱歉，但我没有多少 Python 经验

我有比较文件的功能

def compare_files(file1, file2):
    fname1 = file1
    fname2 = file2

    # Open file for reading in text mode (default mode)
    f1 = open(fname1)
    f2 = open(fname2)
    # Print confirmation
    #print("-----------------------------------")
    #print("Comparing files ", " > " + fname1, " < " +fname2, sep='\n')
    #print("-----------------------------------")

    # Read the first line from the files
    f1_line = f1.readline()
    f2_line = f2.readline()

    # Initialize counter for line number
    line_no = 1

    # Loop if either file1 or file2 has not reached EOF

    while f1_line != '' or f2_line != '':

       # Strip the leading whitespaces
      f1_line = f1_line.rstrip()
      f2_line = f2_line.rstrip()

      # Compare the lines from both file
      if f1_line != f2_line:

         ########## If a line does not exist on file2 then mark the output with + sign
        if f2_line == '' and f1_line != '':
            print ("Line added:Line-%d" % line_no + "-"+ f1_line)
         #otherwise output the line on file1 and mark it with > sign
        elif f1_line != '':
            print ("Line changed:Line-%d" % line_no + "-"+ f1_line)


        ########### If a line does not exist on file1 then mark the output with + sign
        if f1_line == '' and f2_line != '':
            print ("Line removed:Line-%d" % line_no + "-"+ f1_line)
          # otherwise output the line on file2 and mark it with < sign
         #elif f2_line != '':
            #print("<", "Line-%d" %  line_no, f2_line)

         # Print a blank line
         #print()

    #Read the next line from the file
      f1_line = f1.readline()
      f2_line = f2.readline()
      #Increment line counter
      line_no += 1

    # Close the files
    f1.close()
    f2.close()

我想将函数输出打印到文本文件

result=compare_files("1.txt", "2.txt")

print (result)
Line changed:Line-1-aaaaa
Line added:Line-2-sss
None

我试过以下方法：

f = open('changes.txt', 'w')

f.write(str(result))

f.close

但只有 None 被打印到 changes.txt

我正在使用 "workaround" sys.stdout 但想知道有没有其他方法可以代替重定向打印输出。

如果在函数输出中我指定 return 而不是打印，那么我只会得到第一个输出行（第 changed:Line-1-aaaaa 行）到 changes.txt

Answer 1

您的 'compare_files' 函数没有 return 任何内容，因此没有任何内容写入文件。使函数'return'成为某种东西，它应该可以工作。

Answer 2

您的函数没有 returning 任何东西，所以您正在打印“None”。如果您希望所有打印都转到文件而不是默认情况下的标准输出，您可以像对 return 值所做的那样更改每个打印语句。

或者您可以像 here 中那样对整个程序使用重定向。

Answer 3

因为默认情况下您不会返回任何函数 returns None，所以这反映在您的 changes.txt 文件中。您可以创建一个变量来存储您想要的输出并 returns 它。

def compare_files(file1, file2):
    fname1 = file1
    fname2 = file2

    # Open file for reading in text mode (default mode)
    f1 = open(fname1)
    f2 = open(fname2)

    output_string = ""

    # Print confirmation
    # print("-----------------------------------")
    # print("Comparing files ", " > " + fname1, " < " +fname2, sep='\n')
    # print("-----------------------------------")

    # Read the first line from the files
    f1_line = f1.readline()
    f2_line = f2.readline()

    # Initialize counter for line number
    line_no = 1

    # Loop if either file1 or file2 has not reached EOF

    while f1_line != '' or f2_line != '':

        # Strip the leading whitespaces
        f1_line = f1_line.rstrip()
        f2_line = f2_line.rstrip()

        # Compare the lines from both file
        if f1_line != f2_line:

            ########## If a line does not exist on file2 then mark the output with + sign
            if f2_line == '' and f1_line != '':
                print("Line added:Line-%d" % line_no + "-" + f1_line)
                output_string += "Line added:Line-%d" % line_no + "-" + f1_line + "\n"
            # otherwise output the line on file1 and mark it with > sign
            elif f1_line != '':
                print("Line changed:Line-%d" % line_no + "-" + f1_line)
                output_string += "Line changed:Line-%d" % line_no + "-" + f1_line +"\n"

            ########### If a line does not exist on file1 then mark the output with + sign
            if f1_line == '' and f2_line != '':
                print("Line removed:Line-%d" % line_no + "-" + f1_line)
                output_string += "Line removed:Line-%d" % line_no + "-" + f1_line +"\n"
            # otherwise output the line on file2 and mark it with < sign
            # elif f2_line != '':
        # print("<", "Line-%d" %  line_no, f2_line)

        # Print a blank line
        # print()

        # Read the next line from the file
        f1_line = f1.readline()
        f2_line = f2.readline()
        # Increment line counter
        line_no += 1

    # Close the files
    f1.close()
    f2.close()
    return output_string

Answer 4

您的 compare_files() 只是打印，但不会将任何内容传递给调用者。

如果要将一项传递给调用者，请使用 return。您的函数流程到此结束。

如果您想将多个项目传递给呼叫者，您 yield 他们。使用 yield 将您的函数变成生成器函数。调用生成器函数会生成一个可以迭代的生成器对象。

示例：

def produce_strings():
    for i in ['a', 'b', 'c']:
        yield i + "x"

result = "\n".join(produce_strings())
print(result) # prints a line end separated string made of "ax", "bx" and "cx".

Python 将函数输出写入文件

Python write function output to file

python

string-comparison