老男孩python学习自修第九天【yield生成器】

1.如果在一个方法中有yield关键字则该方法返回的是一个生成器对象

2.对生成器对象进行操作必须进行迭代或循环处理

例如：

yield_test.py

#!/usr/bin/env python
# _*_ coding:UTF-8 _*_

def MyReadLines():
    seek = 0
    while True:
        with open('myFile.txt', 'rb') as f:
            f.seek(seek)
            line = f.readline()
            if line:
                seek = f.tell()
                yield line
            else:
                return

if __name__ == "__main__":
    print MyReadLines()
    for line in MyReadLines():
        print line

结果：

/Users/liudaoqiang/PycharmProjects/numpy/venv/bin/python /Users/liudaoqiang/Project/python_project/day09/yield_test.py
<generator object MyReadLines at 0x10f0fd410>
##

# User Database

# 

# Note that this file is consulted directly only when the system is running

# in single-user mode.  At other times this information is provided by

# Open Directory.

#

# See the opendirectoryd(8) man page for additional information about

# Open Directory.

##

nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false

root:*:0:0:System Administrator:/var/root:/bin/sh

daemon:*:1:1:System Services:/var/root:/usr/bin/false

_uucp:*:4:4:Unix to Unix Copy Protocol:/var/spool/uucp:/usr/sbin/uucico

_taskgated:*:13:13:Task Gate Daemon:/var/empty:/usr/bin/false

_networkd:*:24:24:Network Services:/var/networkd:/usr/bin/false

_installassistant:*:25:25:Install Assistant:/var/empty:/usr/bin/false

_lp:*:26:26:Printing Services:/var/spool/cups:/usr/bin/false

_postfix:*:27:27:Postfix Mail Server:/var/spool/postfix:/usr/bin/false

_scsd:*:31:31:Service Configuration Service:/var/empty:/usr/bin/false

_ces:*:32:32:Certificate Enrollment Service:/var/empty:/usr/bin/false

_appstore:*:33:33:Mac App Store Service:/var/empty:/usr/bin/false

_mcxalr:*:54:54:MCX AppLaunch:/var/empty:/usr/bin/false

_appleevents:*:55:55:AppleEvents Daemon:/var/empty:/usr/bin/false

_geod:*:56:56:Geo Services Daemon:/var/db/geod:/usr/bin/false

_serialnumberd:*:58:58:Serial Number Daemon:/var/empty:/usr/bin/false

_devdocs:*:59:59:Developer Documentation:/var/empty:/usr/bin/false

_sandbox:*:60:60:Seatbelt:/var/empty:/usr/bin/false

_mdnsresponder:*:65:65:mDNSResponder:/var/empty:/usr/bin/false

_ard:*:67:67:Apple Remote Desktop:/var/empty:/usr/bin/false

_www:*:70:70:World Wide Web Server:/Library/WebServer:/usr/bin/false

_eppc:*:71:71:Apple Events User:/var/empty:/usr/bin/false

_cvs:*:72:72:CVS Server:/var/empty:/usr/bin/false

_svn:*:73:73:SVN Server:/var/empty:/usr/bin/false

_mysql:*:74:74:MySQL Server:/var/empty:/usr/bin/false

_sshd:*:75:75:sshd Privilege separation:/var/empty:/usr/bin/false

_qtss:*:76:76:QuickTime Streaming Server:/var/empty:/usr/bin/false

_cyrus:*:77:6:Cyrus Administrator:/var/imap:/usr/bin/false

_mailman:*:78:78:Mailman List Server:/var/empty:/usr/bin/false

_appserver:*:79:79:Application Server:/var/empty:/usr/bin/false

_clamav:*:82:82:ClamAV Daemon:/var/virusmails:/usr/bin/false

_amavisd:*:83:83:AMaViS Daemon:/var/virusmails:/usr/bin/false

_jabber:*:84:84:Jabber XMPP Server:/var/empty:/usr/bin/false

_appowner:*:87:87:Application Owner:/var/empty:/usr/bin/false

_windowserver:*:88:88:WindowServer:/var/empty:/usr/bin/false

_spotlight:*:89:89:Spotlight:/var/empty:/usr/bin/false

_tokend:*:91:91:Token Daemon:/var/empty:/usr/bin/false

_securityagent:*:92:92:SecurityAgent:/var/db/securityagent:/usr/bin/false

_calendar:*:93:93:Calendar:/var/empty:/usr/bin/false

_teamsserver:*:94:94:TeamsServer:/var/teamsserver:/usr/bin/false

_