Python:按照指定行数打印文件内容

方法一：先全部读取并存放列表，再通过列表索引迭代打印

实现思路：
1.打开文件
2.读取文件并存储在列表中，方便按指定行数打印文件
3.获取开始和结束位置，并转换为对应列表索引
4.迭代打印列表对应行内容

def print_lines(file_name,lines_num):
    f = open(file_name, "r")
    ###确定开始行和结尾行
    lines_list = lines_num.split(sep = ":")
    start_line = lines_list[0]
    end_line = lines_list[1]
    ###将文件按行排列在列表中方便打印
    f_list = []
    for eachline in f:
        f_list.append(eachline)

    if start_line == "" and end_line == "":
        print(f"文件{file_name}的全文内容如下：")
        start_index = 0
        end_index = len(f_list)
    elif start_line == "":
        print(f"文件{file_name}从开始到第{int(end_line)}行的内容如下：")
        start_index = 0
        end_index = int(end_line)
    elif end_line == "":
        print(f"文件{file_name}从第{int(start_line)}行到末尾的内容如下：")
        end_index = len(f_list)
        start_index = int(start_line) - 1
    else:
        print(f"文件{file_name}从第{int(start_line)}行到{int(end_line)}的内容如下：")
        start_index = int(start_line) - 1
        end_index = int(end_line)
    ####按要求打印文件内容
    for i in range(start_index, end_index):
        print(f_list[i])

    f.close()
        
    
file_name = input(r"请输入要打开的文件(C:\\test.txt)：")
lines_num = input("请输入需要显示文件的行数【格式如13:21或：21或21：】：")
print_lines(file_name,lines_num)

方法二：不通过列表，消耗读取

def print_lines(file_name,lines_num):
    f = open(file_name, "r")
    ###确定开始行和结尾行
    lines_list = lines_num.split(sep = ":")
    start_line = lines_list[0]
    end_line = lines_list[1]


    if start_line == "" and end_line == "":
        print(f"文件{file_name}的全文内容如下：")
        start_index = 0
        end_index = -1
    elif start_line == "":
        print(f"文件{file_name}从开始到第{int(end_line)}行的内容如下：")
        start_index = 0
        end_index = int(end_line)
    elif end_line == "":
        print(f"文件{file_name}从第{int(start_line)}行到末尾的内容如下：")
        end_index = -1
        start_index = int(start_line) - 1
    else:
        print(f"文件{file_name}从第{int(start_line)}行到{int(end_line)}的内容如下：")
        start_index = int(start_line) - 1
        end_index = int(end_line)
    ####按要求打印文件内容
    for i in range(start_index):###用于消耗掉start_index之前的内容
        f.readline()
    if end_index - start_index == -1:#读取全文的条件
        print(f.read())
    else:
        for j in range(end_index - start_index):
            print(f.readline(),end = '')
    
    f.close()
        
    
file_name = input(r"请输入要打开的文件(C:\\test.txt)：")
lines_num = input("请输入需要显示文件的行数【格式如13:21或：21或21：】：")
print_lines(file_name,lines_num)