输入一段英文，用python函数实现统计单词个数；统计标点符号个数；将每个单词逆序，统计字母出现的频率，返回字典等功能

可以使用Python的内置函数和模块来实现这些功能。

1. 统计单词个数和标点符号个数

import string

def count_words(text):
    """
    统计单词个数和标点符号个数
    """
    words = text.split()
    num_words = len(words)
    num_punctuations = sum([1 for char in text if char in string.punctuation])
    return num_words, num_punctuations

2. 将每个单词逆序

def reverse_words(text):
    """
    将每个单词逆序
    """
    words = text.split()
    reversed_words = [word[::-1] for word in words]
    return ' '.join(reversed_words)

3. 统计字母出现的频率，返回字典

def count_letters(text):
    """
    统计字母出现的频率，返回字典
    """
    freq_dict = {}
    for char in text:
        if char.isalpha():
            if char.lower() in freq_dict:
                freq_dict[char.lower()] += 1
            else:
                freq_dict[char.lower()] = 1
    return freq_dict

完整代码如下：

import string

def count_words(text):
    """
    统计单词个数和标点符号个数
    """
    words = text.split()
    num_words = len(words)
    num_punctuations = sum([1 for char in text if char in string.punctuation])
    return num_words, num_punctuations

def reverse_words(text):
    """
    将每个单词逆序
    """
    words = text.split()
    reversed_words = [word[::-1] for word in words]
    return ' '.join(reversed_words)

def count_letters(text):
    """
    统计字母出现的频率，返回字典
    """
    freq_dict = {}
    for char in text:
        if char.isalpha():
            if char.lower() in freq_dict:
                freq_dict[char.lower()] += 1
            else:
                freq_dict[char.lower()] = 1
    return freq_dict

text = "Hello World! This is a sample text for testing purposes."
num_words, num_punctuations = count_words(text)
print("Number of words:", num_words)
print("Number of punctuations:", num_punctuations)

reversed_text = reverse_words(text)
print("Reversed words:", reversed_text)

freq_dict = count_letters(text)
print("Letter frequency:", freq_dict)