在python中直接写入.csv时，如何防止用户输入相同的输入两次

Question

我正在尝试根据用户输入创建数据集。我试图防止其中一个字段重复。我要求用户选择一个与他们的姓名、年龄、gpa 和专业相匹配的字母。我想确保输入的字母是唯一的，但我不确定在直接写入 .csv 文件时如何执行此操作。

这是我目前所拥有的。

import csv
from colorama import Fore, Back, Style


with open('students2.csv', 'w+', newline='') as csvfile:
        columnheaders = ['NAME','AGE','GPA','MAJOR']
        writer = csv.DictWriter(csvfile, fieldnames=columnheaders)

        writer.writeheader()

        for i in range(0,10):
            askname=input('Please select the letter that matches your name from the following:  (A, B, C, D, E, F, G, H, I, J),  ')
            askage=input('Please enter your Age: ')
            askgpa=input('Please enter your GPA: ')
            askmajor=input('Please select your major from the following (CS, CET, CIS, CE) ')
            writer.writerow({'NAME': askname,'AGE': askage,'GPA': askgpa,'MAJOR': askmajor}) 
            print(Back.BLACK +'My name starts with the letter:', askname ,' and I am ', askage, 'years old. I study ', askmajor, 'and my GPA is: ', askgpa)
            print(Style.RESET_ALL)

我知道如何使用列表来做到这一点，

namelist = []

while True:

    #Input name
    while True:
        name = str(input('What is your name? '))
        if name.upper() not in ('A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'):
            print("Please use (A, B, C, D, E, F, G, H, I, J).")
            continue
        if name in namelist:
            print("This name has already been used.")
            continue
        else:
            namelist.append(name)
            break 

但是是否有可能做到这一点而不必通过列表进行然后将其转换为 .csv？

任何帮助将不胜感激。 提前致谢。

Answer 1

您需要在内存中保留一份列表副本（您可以每次都扫描 CSV，但这会导致大量不必要的磁盘 IO）。

我的建议是将名称缓存在一个集合中，因此您可以在脚本顶部添加nameseen = set() 之类的内容，然后在编写该行之前对其进行检查。比如：

if not (askname in nameseen):
    writer.writerow({'NAME': askname,'AGE': askage,'GPA': askgpa,'MAJOR': askmajor}) 
    nameseen.add(askname)

    print(Back.BLACK +'My name starts with the letter:', askname ,' and I am ', askage, 'years old. I study ', askmajor, 'and my GPA is: ', askgpa)
    print(Style.RESET_ALL)
else:
    print("This name has already been used.")

Answer 2

如果你可以使用 pandas，你可以这样做：

import pandas as pd
df = pd.read_csv('kd.csv', index_col=0)
df.to_csv()
# 'NAME,AGE,GPA,MAJOR\nBill,18,4.0,CS\nMike,20,2.9,BS\nWill,20,2.4,CS\nBill,18,4.0,CS\n'

df.drop_duplicates(subset=None, inplace=True)
df.to_csv()
# 'NAME,AGE,GPA,MAJOR\nBill,18,4.0,CS\nMike,20,2.9,BS\nWill,20,2.4,CS\n'

更新

我将其更改为使用您的 cmets 进行更新。一些更新，如果文件不存在则创建文件，并且仍在使用您的 cmets 改进它。如果卡在无限循环中，可以按 CTRL-D。

$ cat kd2.csv
NAME AGE GPA MAJOR
A 20 3.2 CIS
B 31 4.0 CS
C 34 3.5 CE
D 18 2.0 CS
E 4.0 3.2 CE

import io

def new_student_add():
  only_allowed = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']
  stub = io.StringIO('NAME AGE GPA MAJOR\n')
  while True:
     try:
        df = pd.read_csv('kd4.csv', delim_whitespace=True, index_col=0) 
     except:
        stub.seek(0)
        df = pd.read_csv(stub, delim_whitespace=True, index_col=0)
     new_csv_dict = {}
     try:
        new_name =input('Please select the letter that matches your name from the following:  (A, B, C, D, E, F, G, H, I, J):  ')
     except:
        break
     if new_name not in only_allowed:
        print("Only letters in {} are allowed".format(only_allowed))
        continue
     if  new_name in df.index: 
        print("This name has already been used.")
        continue
     new_csv_dict['AGE'] =input('Please enter your Age: ')
     new_csv_dict['GPA'] =input('Please enter your GPA: ')
     new_csv_dict['MAJOR'] =input('Please select your major from the following (CS, CET, CIS, CE) ')
     df.loc[new_name] = new_csv_dict   
     break 
  df.to_csv(r'kd4.csv', sep=' ')
  return df 

for x in range (0,9):
   df = new_student_add()


for name, row in  df.iterrows(): 
  print("My name starts with the letter {} and I am {} years old. I study {} and my GPA is: {}".format(name, int(row['AGE']), row['MAJOR'], row['GPA']))

# This may be much faster, so adding it in in case the author needs a faster algorithm. Thanks AlexanderCécile
# for item in df.itertuples(): 
# print(f"My name starts with the letter {item[0]} and I am {item[1]} years old. I study {item[3]} and my GPA is: {item[2]}")