如何在“列印陳述句”之前在for回圈中執行“if陳述句”

我對 Python 中的檔案處理和 csv 檔案相當陌生。

代碼

import csv
file1=open("Employee.csv","w",newline='\r\n')
empwriter=csv.writer(file1)
empwriter.writerow(["EmpID.","Name","MobNo."])
n=int(input("How many employee records do you want to add?:"))
for i in range(n):
    print("\nEmployee Record",(i 1))
    empid=input("Enter empID:")
    name=input("Enter Name:")
    mob=input("Enter Mobile No.:")
    emprec=[empid,name,mob]
    empwriter.writerow(emprec)
file1.close()

file2=open("Employee.csv","r ",newline='\r\n')
empreader=csv.reader(file2)
newwriter=csv.writer(file2)
check=input("\nEnter the empID to check:\n")
opt=int(input('''Which of the following fields do you want to update?:
1.Update the Name
2.Update the Mobile No.
3Update the whole record\n\n'''))

if opt==1:
    for x in empreader:
        if x[0]==check:
            newname=input("Enter new name:")
            x[1]=newname
            print("Record Updated Successfully!\n Updated record:\n",x)
            newwriter.writerow(x)
        print(x)
elif opt==2:
    for x in empreader:
        if x[0]==check:
            newmob=input("Enter new Mobile No.:")
            x[2]=newmob
            print("Record Updated Successfully!\n Updated record:\n",x)
            newwriter.writerow(x)
        print(x)     
elif opt==3:
    for x in empreader:
        if x[0]==check:
            newname=input("Enter new name:")
            newmob=input("Enter new Mobile No.:")
            x[1]=newname
            x[2]=newmob
            print("Record Updated Successfully!\n Updated record:\n",x)
            newwriter.writerow(x)
        print(x)
file2.close()

我在這段代碼中試圖

1. 按用戶輸入記錄（empID、Name、MobNo.）并制作一個 csv 檔案。
2. 使用 empID 查找所需的記錄。
3. 更新那個記錄。
4. 顯示所有記錄。

當我執行代碼時，for 回圈中的列印陳述句在 if 陳述句之前執行并給我這個輸出。

輸出

How many employee records do you want to add?:3

Employee Record 1
Enter empID:001
Enter Name:John
Enter Mobile No.:1234567890

Employee Record 2
Enter empID:002
Enter Name:Jane
Enter Mobile No.:2345678901

Employee Record 3
Enter empID:003
Enter Name:Judy
Enter Mobile No.:4567890123

Enter the empID to check:
002
Which of the following fields do you want to update?:
1.Update the Name
2.Update the Mobile No.
3.Update the whole record

2
['EmpID.', 'Name', 'MobNo.']
['001', 'John', '1234567890']
Enter new Mobile No.:1111222233
Record Updated Successfully!
 Updated record:
 ['002', 'Jane', '1111222233']
['002', 'Jane', '1111222233']

正如您在輸出的最后幾行中看到的那樣。Print 陳述句在 if 陳述句（或類似的東西）之前執行。我實際上希望輸出以下面給定的方式顯示......

期望輸出

2
Enter new Mobile No.:1111222233
Record Updated Successfully!
 Updated record:
 ['002', 'Jane', '1111222233']
['EmpID.', 'Name', 'MobNo.']
['001', 'John', '1234567890']
['002', 'Jane', '1111222233']
['003', 'Judy', '4567890123']

uj5u.com熱心網友回復：

我可以看到正在發生的事情，以及為什么它不是您所期望的。

看看這個塊：

elif opt==2:
    for x in empreader:
        if x[0]==check:
            newmob=input("Enter new Mobile No.:")
            x[2]=newmob
            print("Record Updated Successfully!\n Updated record:\n",x)
            newwriter.writerow(x)
        print(x)  

什么是實際發生的情況是，對于每一行x中empreader：

1. ID col, x[0], 正在根據您輸入的 ID 進行評估check。如果匹配：
   1. 你中斷回圈，并介入修改 x
   2. 寫出新值， newwriter.writerow(x)
   3. 然后你走出去......
2. 列印您的更新， print(x)

除非，x[0]==checkis False，在這種情況下x只是列印。

考慮（并測驗）當您為check...提供不存在的 ID 時會發生什么......它永遠不會進入您的“修改界面”，而只會列印empreader.

那么會發生什么，您是否顯示錯誤訊息讓用戶知道他們選擇了錯誤的 ID？

這是一個相當大的變化，但我認為它使邏輯和你的意圖更加清晰......你不是在回圈中做出決定，這非常困難。以“扁平”的順序接受輸入并做出決定：

import csv
import sys

# Get the employee ID
check=input("\nEnter the empID to check:\n")

# and check the ID in the employee records
emp_row = None
with open("Employee.csv","r",newline='\r\n') as f:
    empreader=csv.reader(f)

    for x in empreader:
        if x[0] == check:  # the employee ID matches
            emp_row = x[:]

if emp_row is None:
    print(f'Could not find employee ID {check}')
    sys.exit(0)  # or exit(1) to show it's an "error"

# Now you know you have a valid ID, because emp_row has data

opt=int(input('''Which of the following fields do you want to update?:
1.Update the Name
2.Update the Mobile No.
3.Update the whole record\n\n'''))

if opt == 1:
    newname = input("Enter new name:")
    emp_row[1] = newname
# else if opt == 2:
#    ...
# else if opt ==3:
#    ...

# Now how do you overwrite the old row in Employee.csv with emp_row?
# Don't try to "modify" the original file as you're reading it, instead...
# Read from the old file, copying all the old rows, except for emp_row, to a new list

new_rows = []
with open('Employee.csv', 'r', newline='\r\n') as f_in:
    reader = csv.reader(f_in)
    header_row = next(reader)
    new_rows.append(header_row)

    for row in reader:
        if row[0] == check:
            new_rows.append(emp_row)
        else:
            new_rows.append(row)

# Then write your new_rows out
with open('Employee.csv', 'w', newline='\r\n') as f_out:
    writer = csv.writer(f_out)
    writer.writerows(new_rows)

我從Employee.csv開始，看起來像這樣：

EmpID.,Name,MobNo.
001,John,1234567890
002,Jane,2345678901
003,Judy,4567890123

我運行了它，它看起來像這樣：

% python3 main.py

Enter the empID to check:
002
Which of the following fields do you want to update?:
1.Update the Name
2.Update the Mobile No.
3.Update the whole record

1
Enter new name:Alice

and Employee.csv now looks like:

EmpID.,Name,MobNo.

001,John,1234567890

002,Alice,2345678901

003,Judy,4567890123

(I'm on a Mac, so \r\n adding lines)

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