Python學習筆記 檔案和異常

1、從檔案中讀取資料

#關鍵字with在不需要訪問檔案後自動將其關閉

#open('pi_digits.txt')返回乙個表示檔案pi_digits.txt的物件，並將該物件儲存在變數file_object中
#file_object.read()讀取該檔案物件對應檔案的全部內容
#contents.rstrip()，由於read()讀取到檔案末尾時返回乙個空字串，rstrip()用於刪除該空字串
with
open
('pi_digits.txt'
)as file_object:
contents = file_object.read(
)print
(contents.rstrip(
))

filename =

'pi_digits.txt'
with
open
(filename)
as file_object:
for line in file_object:
print
(line.rstrip(
))

filename =

'pi_digits.txt'
#由於在with中返回的檔案物件只在with**塊中可用
#如果要在with**塊外訪問檔案的內容，可將檔案每行儲存在列表中
with
open
(filename)
as file_object:
lines = file_object.readlines(
)for line in lines:
print
(line.rstrip(
))

filename =

'programming.txt'
#以寫入模式'w'開啟檔案，如果檔案不存在，則建立該檔案，若已存在則清空檔案內容
with
open
(filename,
'w')
as file_object:
file_object.write(
"i love you."
)

#以附加模式'a'開啟檔案，能夠在檔案末尾寫入檔案

with
open
(filename,
'a')
as file_object:
file_object.write(
"i love you.\n"
)	file_object.write(
"what about you?\n"
)

將可能引發異常的**放在try**塊中

將異常處理的**放在except**塊中

try

:print(9
/0)except zerodivisionerror:
print
("you can't divide by zero!"
)

print

("give me two numbers, and i'll divide them."
)print
("enter 'q' to quit."
)while
true
:	first_number =
input
("\nfirst number: "
)	second_number =
input
("\nsecond number: "
)if first_number ==
'q'or second_number ==
'q':
break
try:
answer =
int(first_number)
/int
(second_number)
except zerodivisionerror:
print
("you can't divide by 0!"
)else
:print
(answer)

def

count_words
(filename)
:'''計算乙個檔案大概有多少個單詞'''
try:
with
open
(filename)
as file_object:
contents = file_object.read(
)except filenotfounderror:
# msg = "sorry, the file " + filename + " does not exist."
# print(msg)
pass
else
:#計算檔案中包含多少個單詞
words = contents.split(
)		num_words =
len(words)
print
("the file "
+ filename +
" has about "
+str
(num_words)
+" words."
)#計算檔案中包含多少個'you' 
you_count = words.count(
'you'
)print
("'you': "
+str
(you_count))		
filename =
'alice.txt'
count_words(filename)

import json

numbers =[2
,3,5
,7,11
,13]filename =
'numbers.json'
with
open
(filename,
'w')
as f_obj:
json.dump(numbers, f_obj)

import json

filename =
'numbers.json'
with
open
(filename)
as f_obj:
numbers = json.load(f_obj)
print
(numbers)

import json 

#如果以前儲存了使用者名稱，就載入它
#否則，就提示使用者輸入使用者名稱儲存它
filename =
'username.json'
try:
with
open
(filename)
as f_obj:
username = json.load(f_obj)
except filenotfounderror:
username =
input
("what's your name? "
)with
open
(filename,
'w')
as f_obj:
json.dump(username, f_obj)
print
("we'll remember you when you come back, "
+ username +
"!")
else
:print
("welcome back, "
+ username +
"!")

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