附加到每条打印的消息

Question

简单的问题，我想在我调用的每个print 前面附加文本，例如，如果我将文本设置为hello 并运行：

print 'hello there'
print ' hi again'

它会打印这个：

hellohello there
hello hi again

有什么方法可以做到这一点，而不使用函数来使用它而不是print？

Answer 1

您可以按照DevPlayer's post here on StackOverflow 覆盖打印，此处稍作修改：

from __future__ import print_function
# Note: If you are using Python 3 leave this line out
# This must be the first statement before other statements.
# You may only put a quoted or triple quoted string, 
# Python comments or blank lines before the __future__ line.
import sys

def print(*args, **kwargs):
    """My custom print() function."""
    # Adding new arguments to the print function signature 
    # is probably a bad idea.
    # Instead consider testing if custom argument keywords
    # are present in kwargs
    sys.stdout.write('hello')
    return __builtins__.print(*args, **kwargs)

print ("hello there")
print (" hi again")

[Edit] ...或者正如 DSM 建议的那样，您可以通过以下方式避免 sys 调用：

from __future__ import print_function
# Note: If you are using Python 3 leave this line out
# This must be the first statement before other statements.
# You may only put a quoted or triple quoted string, 
# Python comments or blank lines before the __future__ line.

def print(*args, **kwargs):
    """My custom print() function."""
    # Adding new arguments to the print function signature 
    # is probably a bad idea.
    # Instead consider testing if custom argument keywords
    # are present in kwargs
    __builtins__.print('hello',end='')
    return __builtins__.print(*args, **kwargs)

print ("hello there")
print (" hi again")

Answer 2

您无法更改 Python 2 的打印语句，但您可以编写自己的类似文件的对象并使用它：

class PrefixedFile(object):
    def __init__(self, f, prefix):
        self.f = f
        self.prefix = prefix

    def write(self, s):
        s = s.replace("\n", "\n"+self.prefix)
        self.f.write(s)

sys.stdout = PrefixedFile(sys.stdout, "hello: ")

print "One"
print "Two"

请注意，这段代码不太有效，因为它在第一行缺少一个前缀，并在最后添加了一个，但你明白了！ :)

Answer 3

即使 Jon Cage 的回答是替换 print() 函数的好方法，我还是建议改用您自己的打印函数（使用 Jon 的代码）：

from __future__ import print_function
# Note: If you are using Python 3 leave this line out
# This must be the first statement before other statements.
# You may only put a quoted or triple quoted string, 
# Python comments or blank lines before the __future__ line.

def my_print(*args, **kwargs):
    """My custom print() function."""
    # Adding new arguments to the print function signature 
    # is probably a bad idea.
    # Instead consider testing if custom argument keywords
    # are present in kwargs
    print('hello', end='')
    print(*args, **kwargs)

与 Jon 的答案的唯一区别是您不要覆盖内置的 print()（“猴子补丁”）。我提倡这样做而不是修改print()，因为这使您的代码更易于维护，因为每个人都希望print() 是内置的。

在my_print() 中使用print() 函数 代替print 语句，得到greater flexibility。