固定长度记录

Question

我正在介绍如何使用 python 编写脚本类。我没有编程经验，所以我只知道该课程所教的内容，主要是 for 和 while 循环、基本函数、列表/字典以及当前的正则表达式和文件处理。

我收到了一个我必须打开的文件 P。我必须搜索变量 F（名字）和 L（姓氏），然后将关联的生日切换到 F，将 L 切换到 B（生日）。

每个名字的长度为 16 个字符。每个姓氏长度为 16 个字符。每个生日长度为 8 个字符。因此，每条记录的长度正好是 40 个字符。

下面的代码是我迄今为止将文件放入二维列表的代码。然后我如何搜索列表以找到 F 和 L？找到F和L后，如何将生日切换到B？希望这一切都有意义。提前谢谢你。

import re
file = open (P, 'r')
data = file.read()

records = []
while len(data) > 0:
  record = []
  record.append(data[0:16])
  record.append(data[16:32])
  record.append(data[32:40])
  records.append(record)
  data = data[40:]

Answer 1

我假设“切换与 F 和 L 关联的生日”是指“获取 F 和 L 的生日”

您已经在表单中创建了一个列表列表：

[
 [F1, L1, B1],
 [F2, L2, B2],
 [F3, L3, B3],
 [F4, L4, B4]
]

您必须遍历第一个列表，并比较记录的第一个和第二个元素以匹配您想要的 F 和 L：

for r in records:
  if r[0] == F and r[1] == L:  # List indices starts from 0
    return r[2]

如果您不在函数内部，则不能return，因此需要时break。

Answer 2

@Dustin 这应该可以帮助您完成正在完成的挑战。

name_length = 16
b_length = 8
start = 0
record_count = 0
records = []

# KISS Method - 2nd Attempt - Read in 16, 16, 8 and output to file

for i in range(start, len(data)):
  record = data[start:start + name_length] 
  records.append(record[0:16])
  start += name_length

  record = data[start:start + name_length]
  records.append(record[0:16])
  start += name_length

  record = data[start:start + b_length]
  records.append(record[0:8])
  start += b_length

  record_count += 1

file1.close()

Answer 3

Dustin - 对于 2D 列表 - 您需要使用以下内容 - 我认为这可行。

# Loads the file at filepath 
# Returns a 2d array with the data
# 
def load2dArrayFromFile(filepath):
  file = open(filepath, 'r')
  data = file.read()
  lines = data.split("\n")
  for i in range(0, len(lines)):
    lines[i] = lines[i].split("|")

  return lines

# Searches the 2d array 'records' for firstname, lastname.
# Returns the index of the record or -1 if no record exists
# 
def findIndex(records, firstname, lastname):
  for i in range(0, len(records)):
    if (records[i][0] == firstname and records[i][1] == lastname):
      return [i]
    return -1

# Sets the birthday of the record at the given index
# Returns: nothing
def setBirthday(records, index, newBirthday):
  if (index >= 0):
    records[index][2] = newBirthday

# Convert the 2d array back into a string
# Return the text of the 2d array
def makeTextFrom2dArray(records):
  for i in range(0, len(records)):
    records[i] = "|".join(records)
  return ("\n".join(records))

# ----------------------------------------------------------------
# 
#  Our main code body, where we call our functions.
#  
# ----------------------------------------------------------------

# Load our records from the file into a 2d array
records= load2dArrayFromFile(P)

# Find out which index, if any, has the name we are hunting
indexWeAreHunting= findIndex(records, F, L)

# Set the birthday record to the one we were passed
setBirthday(records, indexWeAreHunting, B)

# Convert the records into a text string
output= makeTextFrom2dArray(records)

# write the text string out to the file