Python導入解釋

Question

難以置信地圍繞着Python導入。我已經讀過了導入X和X導入*這裏的區別 - http://effbot.org/zone/import-confusion.htm，但我很難理解導入「模塊」和「模塊」導入*之間的區別。特別是因爲effbot文章建議堅持使用導入「模塊」，這在這裏不起作用。

此代碼

import csv 
import time 
import datetime 

startdate = time.strptime('31-Dec-50', "%d-%b-%y") 
enddate = time.strptime('1-Jan-00', "%d-%b-%y") 

with open('Classroom Utilization.csv', 'rb') as csvfile: 
     file = csv.DictReader(csvfile, delimiter=',') 
     for row in file: 
      checkstartdate = time.strptime(row['startdate'], "%d-%b-%y") 
      checkenddate = time.strptime(row['enddate'], "%d-%b-%y") 

      if checkstartdate < startdate: 
        startdate = checkstartdate 
      if checkenddate > enddate: 
        enddate = checkenddate 

print time.strftime("%d-%b-%y", startdate) 
print time.strftime("%d-%b-%y", enddate) 

print "pre convert: " + str(startdate) 
print "pre convert: " + str(enddate) 

startdate = datetime.fromtimestamp(mktime(startdate)) 
enddate = datetime.fromtimestamp(mktime(enddate)) 

print "post convert: " + str(startdate) 
print "post convert: " + str(enddate) 

print '%s/%s/%s' % (startdate.month, startdate.day , startdate.year) 

返回該錯誤

File "deconflict.py", line 29, in <module> 
    startdate = datetime.fromtimestamp(mktime(startdate)) 
AttributeError: 'module' object has no attribute 'fromtimestamp' 

從文檔（https://docs.python.org/2/library/datetime.html?highlight=datetime#module-datetime），datetime模塊的日期時間對象有方法fromtimestamp，但進口並沒有讓我用它。

另一方面，使用從模塊導入*修復所有問題。雖然我不明白爲什麼從時間導入*允許我只使用strptime（），但從datetime導入*我仍然必須說datetime.fromtimestamp。

import csv 
from time import * 
from datetime import * 

startdate = strptime('31-Dec-50', "%d-%b-%y") 
enddate = strptime('1-Jan-00', "%d-%b-%y") 

with open('Classroom Utilization.csv', 'rb') as csvfile: 
     file = csv.DictReader(csvfile, delimiter=',') 
     for row in file: 
      checkstartdate = strptime(row['startdate'], "%d-%b-%y") 
      checkenddate = strptime(row['enddate'], "%d-%b-%y") 

      if checkstartdate < startdate: 
        startdate = checkstartdate 
      if checkenddate > enddate: 
        enddate = checkenddate 

print strftime("%d-%b-%y", startdate) 
print strftime("%d-%b-%y", enddate) 

print "pre convert: " + str(startdate) 
print "pre convert: " + str(enddate) 

startdate = datetime.fromtimestamp(mktime(startdate)) 
enddate = datetime.fromtimestamp(mktime(enddate)) 

print "post convert: " + str(startdate) 
print "post convert: " + str(enddate) 

print '%s/%s/%s' % (startdate.month, startdate.day , startdate.year) 

Answer 1

在此特定情況下，datetime模塊具有datetime類。這很令人困惑，因爲它們具有相同的名稱。當你做import datetime時，你會得到一個名爲datetime的模塊。要訪問該模塊的成員（如datetime類），你需要完全限定它（例如：datetime.datetime）

例如：

import datetime 
startdate = datetime.datetime.fromtimestamp(mktime(startdate)) 

當你from datetime import *，由datetime引用的就是不是模塊，而是同名的類。你得到相同的對象，如果你沒有from datetime import datetime，這意味着「從日期時間模塊導入日期時間類」

Answer 2

datetime模塊之內具有DateTime類。這是你將如何使用它

from datetime import * 
datetime.datetime.fromtimestamp 

或

from datetime import datetime 
datetime.fromtimestamp 

時模塊沒有時間類直接公開它的方法。