非程式設計師 Python 3 教程/檔案 I/O
這是一個簡單的檔案 I/O (輸入/輸出) 示例
# Write a file
with open("test.txt", "wt") as out_file:
out_file.write("This Text is going to out file\nLook at it and see!")
# Read a file
with open("test.txt", "rt") as in_file:
text = in_file.read()
print(text)
輸出和檔案 test.txt 的內容是
This Text is going to out file Look at it and see!
請注意，它在您執行程式的目錄中寫入了一個名為 test.txt 的檔案。字串中的 \n 告訴 Python 在它出現的地方插入一個換行符。
檔案 I/O 的概述是
- 使用
open函式獲取檔案物件 - 讀寫檔案物件（取決於開啟方式）
- 如果您沒有使用
with開啟檔案，您需要手動關閉它
第一步是獲取檔案物件。實現此目的的方法是使用 open 函式。格式為 file_object = open(filename, mode)，其中 file_object 是要放置檔案物件的變數，filename 是包含檔名（字串），mode 是 "rt" 以讀取檔案為文字，或 "wt" 以寫入檔案為文字（以及其他一些我們將在此處跳過的內容）。接下來，可以呼叫檔案物件函式。兩個最常見的函式是 read 和 write。write 函式將字串新增到檔案的末尾。read 函式讀取檔案中下一個內容，並將其作為字串返回。如果沒有給出引數，它將返回整個檔案（如示例中所示）。
現在，我們之前製作的電話號碼程式的新版本
def print_numbers(numbers):
print("Telephone Numbers:")
for k, v in numbers.items():
print("Name:", k, "\tNumber:", v)
print()
def add_number(numbers, name, number):
numbers[name] = number
def lookup_number(numbers, name):
if name in numbers:
return "The number is " + numbers[name]
else:
return name + " was not found"
def remove_number(numbers, name):
if name in numbers:
del numbers[name]
else:
print(name," was not found")
def load_numbers(numbers, filename):
in_file = open(filename, "rt")
while True:
in_line = in_file.readline()
if not in_line:
break
in_line = in_line[:-1]
name, number = in_line.split(",")
numbers[name] = number
in_file.close()
def save_numbers(numbers, filename):
out_file = open(filename, "wt")
for k, v in numbers.items():
out_file.write(k + "," + v + "\n")
out_file.close()
def print_menu():
print('1. Print Phone Numbers')
print('2. Add a Phone Number')
print('3. Remove a Phone Number')
print('4. Lookup a Phone Number')
print('5. Load numbers')
print('6. Save numbers')
print('7. Quit')
print()
phone_list = {}
menu_choice = 0
print_menu()
while True:
menu_choice = int(input("Type in a number (1-7): "))
if menu_choice == 1:
print_numbers(phone_list)
elif menu_choice == 2:
print("Add Name and Number")
name = input("Name: ")
phone = input("Number: ")
add_number(phone_list, name, phone)
elif menu_choice == 3:
print("Remove Name and Number")
name = input("Name: ")
remove_number(phone_list, name)
elif menu_choice == 4:
print("Lookup Number")
name = input("Name: ")
print(lookup_number(phone_list, name))
elif menu_choice == 5:
filename = input("Filename to load: ")
load_numbers(phone_list, filename)
elif menu_choice == 6:
filename = input("Filename to save: ")
save_numbers(phone_list, filename)
elif menu_choice == 7:
break
else:
print_menu()
print("Goodbye")
請注意，它現在包含檔案儲存和載入功能。以下是我的執行程式兩次後的輸出
1. Print Phone Numbers 2. Add a Phone Number 3. Remove a Phone Number 4. Lookup a Phone Number 5. Load numbers 6. Save numbers 7. Quit Type in a number (1-7): 2 Add Name and Number Name: Jill Number: 1234 Type in a number (1-7): 2 Add Name and Number Name: Fred Number: 4321 Type in a number (1-7): 1 Telephone Numbers: Name: Jill Number: 1234 Name: Fred Number: 4321 Type in a number (1-7): 6 Filename to save: numbers.txt Type in a number (1-7): 7 Goodbye
1. Print Phone Numbers 2. Add a Phone Number 3. Remove a Phone Number 4. Lookup a Phone Number 5. Load numbers 6. Save numbers 7. Quit Type in a number (1-7): 5 Filename to load: numbers.txt Type in a number (1-7): 1 Telephone Numbers: Name: Jill Number: 1234 Name: Fred Number: 4321 Type in a number (1-7): 7 Goodbye
該程式的新的部分是
def load_numbers(numbers, filename):
in_file = open(filename, "rt")
while True:
in_line = in_file.readline()
if not in_line:
break
in_line = in_line[:-1]
name, number = in_line.split(",")
numbers[name] = number
in_file.close()
def save_numbers(numbers, filename):
out_file = open(filename, "wt")
for k, v in numbers.items():
out_file.write(k + "," + v + "\n")
out_file.close()
首先，我們將檢視程式的儲存部分。首先，它使用命令 open(filename, "wt") 建立一個檔案物件。接下來，它遍歷併為每個電話號碼建立一個行，使用命令 out_file.write(k + "," + v + "\n")。這將寫入包含姓名、逗號、號碼和換行符的一行。
載入部分稍微複雜一些。它首先獲取檔案物件。然後，它使用 while True: 迴圈，一直迴圈直到遇到 break 語句。接下來，它使用 in_line = in_file.readline() 獲取一行。readline 函式在到達檔案末尾時將返回一個空字串。if 語句檢查這一點，並在發生這種情況時從 while 迴圈中 break。當然，如果 readline 函式沒有返回行尾的換行符，則無法判斷空字串是空行還是檔案末尾，因此換行符保留在 readline 返回的內容中。因此，我們必須去掉換行符。行 in_line = in_line[:-1] 透過刪除最後一個字元來實現這一點。接下來，行 name, number = in_line.split(",") 在逗號處將行拆分為名稱和號碼。然後將其新增到 numbers 字典中。
你可能會對自己說，“好吧，我知道如何讀寫文字檔案，但如果我想列印檔案而不開啟另一個程式，怎麼辦？”
有幾種不同的方法可以實現這一點。最簡單的方法確實會開啟另一個程式，但所有操作都在 Python 程式碼中處理，不需要使用者指定要列印的檔案。此方法涉及呼叫另一個程式的子程序。
還記得我們在上面程式中寫入輸出的檔案嗎？讓我們使用該檔案。請記住，為了防止一些錯誤，此程式使用了下一章中的概念。請隨時在下一章之後重新訪問此示例。
import subprocess
def main():
try:
print("This small program invokes the print function in the Notepad application")
#Lets print the file we created in the program above
subprocess.call(['notepad','/p','numbers.txt'])
except WindowsError:
print("The called subprocess does not exist, or cannot be called.")
main()
subprocess.call 接受三個引數。在本文件的示例中，第一個引數應該是您要從中呼叫列印子程序的程式名稱。第二個引數應該是該程式中的特定子程序。為簡單起見，只需瞭解在本文件中，'/p' 是用於透過指定應用程式訪問印表機的子程序。最後一個引數應該是您要傳送到列印子程序的檔名稱。在本例中，它與本章前面使用的檔案相同。
現在修改字典部分中的成績程式，使其使用檔案 I/O 來儲存學生的記錄。
解決方案
現在修改字典部分中的成績程式，使其使用檔案 I/O 來儲存學生的記錄。
assignments = ['hw ch 1', 'hw ch 2', 'quiz ', 'hw ch 3', 'test']
students = { }
def load_grades(gradesfile):
inputfile = open(gradesfile, "r")
grades = [ ]
while True:
student_and_grade = inputfile.readline()
student_and_grade = student_and_grade[:-1]
if not student_and_grade:
break
else:
studentname, studentgrades = student_and_grade.split(",")
studentgrades = studentgrades.split(" ")
students[studentname] = studentgrades
inputfile.close()
print("Grades loaded.")
def save_grades(gradesfile):
outputfile = open(gradesfile, "w")
for k, v in students.items():
outputfile.write(k + ",")
for x in v:
outputfile.write(str(x) + " ")
outputfile.write("\n")
outputfile.close()
print("Grades saved.")
def print_menu():
print("1. Add student")
print("2. Remove student")
print("3. Load grades")
print("4. Record grade")
print("5. Print grades")
print("6. Save grades")
print("7. Print Menu")
print("9. Quit")
def print_all_grades():
if students:
keys = sorted(students.keys())
print('\t', end=' ')
for x in assignments:
print(x, '\t', end=' ')
print()
for x in keys:
print(x, '\t', end=' ')
grades = students[x]
print_grades(grades)
else:
print("There are no grades to print.")
def print_grades(grades):
for x in grades:
print(x, '\t', end=' ')
print()
print_menu()
menu_choice = 0
while menu_choice != 9:
print()
menu_choice = int(input("Menu Choice: "))
if menu_choice == 1:
name = input("Student to add: ")
students[name] = [0] * len(assignments)
elif menu_choice == 2:
name = input("Student to remove: ")
if name in students:
del students[name]
else:
print("Student:", name, "not found")
elif menu_choice == 3:
gradesfile = input("Load grades from which file? ")
load_grades(gradesfile)
elif menu_choice == 4:
print("Record Grade")
name = input("Student: ")
if name in students:
grades = students[name]
print("Type in the number of the grade to record")
print("Type a 0 (zero) to exit")
for i,x in enumerate(assignments):
print(i + 1, x, '\t', end=' ')
print()
print_grades(grades)
which = 1234
while which != -1:
which = int(input("Change which Grade: "))
which -= 1
if 0 <= which < len(grades):
grade = input("Grade: ") # Change from float(input()) to input() to avoid an error when saving
grades[which] = grade
elif which != -1:
print("Invalid Grade Number")
else:
print("Student not found")
elif menu_choice == 5:
print_all_grades()
elif menu_choice == 6:
gradesfile = input("Save grades to which file? ")
save_grades(gradesfile)
elif menu_choice != 9:
print_menu()