Python：打印函數文本的自定義打印函數

Question

蟒蛇腳本：

text = "abcde"
print("text[::-1] : ", text[::-1])
print("text[5:0:-1] : ", text[5:0:-1])

輸出：

text[::-1] :  edcba
text[5:0:-1] :  edcb

可以定義一個自定義函數來避免輸入重復嗎？ 例如：

text = "abcde"
def fuc(x):
    print(x, ":", x)
    
fuc(text[::-1])
fuc(text[5:0:-1])

要求。 輸出：

text[::-1] :  edcba
text[5:0:-1] :  edcb

Answer 1

在python 3.8+中，您可以使用自記錄表達式

>>> print(f"{a[::-1]=}") 
a[::-1]='edcba'

Answer 2

使用 f-strings 可以實現涉及字符串插值的解決方案。 但是，f 字符串僅適用於 Python 3.8+

但是，我們可以輕松地實現字符串插值，如How to Implement String Interpolation in Python 中所述

Current Modification 擴展了上述引用，以允許除了變量查找之外的表達式。

import sys
from re import sub

def interp(s):
  '''Implement simple string interpolation to handle
    "{var}" replaces var with its value from locals
    "{var=}" replaces var= with var=value, where value is the value of var from locals
    "{expressions} use eval to evaluate expressions (make eval safe by only allowing items from local functions and variables in expression'''

  # 1. Implement self-documenting expressions similar to https://docs.python.org/3/whatsnew/3.8.html#f-strings-support-for-self-documenting-expressions-and-debugging
  s1 = sub( r'{\s*(.*?)=\s*}', lambda m: m.group(1) + '=' + '{' + m.group(1) + '}', s)

  # Get the locals from the previous frame
  previous_frame = sys._getframe(1)  # i.e. current frame(0), previous is frame(1)
  d = previous_frame.f_locals        # get locals from previous frame

  # 2--Replace variable and expression with values
  # Use technique from http://lybniz2.sourceforge.net/safeeval.html to limit eval to make it safe
  # by only allowing locals from d and no globals
  s2 = sub(r'{\s*([^\s]+)\s*}', lambda m: str(d[m.group(1)]) if m.group(1) in d else str(eval(m.group(1), {}, d)), s1)
  return s2

# Test
a = "abcde"

print(interp("a has value {a}"))  # without self-doc =
#Output>>> a has value abcde

print(interp("{a[::-1]=}"))       # with self-doc =
#Output>>> a[::-1]=edcba

print(interp('{a[4:0:-1]=}'))     # with self-doc =
#Output>>> a[4:0:-1]=edcb

print(interp('sum {1+1}') # without self-doc =
#Output>>> sum 2

print(interp('{1+1=}'))  # with self-doc =
#Output>>> 1+1=2