python23等于多少python中～1等于多少

python23等于多少python中～1等于多少

本篇文章首席CTO笔记来给大家介绍有关python23等于多少以及python中～1等于多少的相关内容，希望对大家有所帮助，一起来看看吧。
本文目录一览：
1、为什么Python中print(eval(input(3+4*5)))输出为23？2、python函数返回值为”id“：“23”，如何获取233、python运算符为什么Python中print(eval(input(3+4*5)))输出为23？一步一步分解：
1 计算Input(3+4*5)得到的是：'3+4*5'
2 使用eval可以计算字符表达式的值，所以是3+4*5=3+20=23
python函数返回值为”id“：“23”，如何获取23最近遇到os.system()执行系统命令的情况，上网搜集了一下资料，整理如下，以备不时之需，同时也希望能帮到某些人。
一、python中的 os.system(cmd)的返回值与linux命令返回值（具体参见本文附加内容）的关系
大家都习惯用os.systemv()函数执行linux命令，该函数的返回值十进制数（分别对应一个16位的二进制数）。该函数的返回值与 linux命令返回值两者的转换关系为：该函数的返回值（十进制）转化成16二进制数，截取其高八位（如果低位数是0的情况下，有关操作系统的错误码共 131个，所以低位都是零），然后转乘十进制数即为 linux命令返回值0。
例如：
os.system()返回值为0linux命令返回值也为0.
os.system()返回值为256，十六位二进制数示为：00000001，00000000，高八位转乘十进制为 1 对应 linux命令返回值 1
os.system()返回值为512，十六位二进制数示为：00000010，00000000，高八位转乘十进制为 2 对应 linux命令返回值 2
......其它同理
os.system()返回值为32512，十六位二进制数示为：01111111，00000000，高八位转乘十进制为 127对应 linux命令返回值 127
........
/**********************************************************************************************************************/
问题：/bin/xxx.py是一个返回码为1的程序。当python 程序使用os.system(”./bin/xxx.py”) 这样调用的时候， 成功运行后os.system 的返回值出现了问题，变成了256 ，也就是0×100。而不是正常应该返回的1。
解决：查阅了文档发现os.system()的返回为：
On Unix, the return value is the exit status of the process encoded in the format specified for wait().
而os.wait()的返回为：
a 16-bit number, whose low byte is the signal number that killed the process, and whose high byte is the exit status (if the signal number
is zero);
os.system的返回值并不是执行程序的返回结果。而是一个16位的数，它的高位才是返回码。也就是说os.system()返回256即 0×0100，返回码应该是其高位0×01即1。所以要获取程序运行退出的值（比如C的main函数中的return 0），需要处理一下。
ret = os.system('./a.out')
ret = 8
这样才能获取到正确的返回值。另外还要注意：python获取到的值是无符号整数，所以返回负值的时候，打印出来是很大的正值。比如返回-1，python 会获取到255，-2则254，以此类推。所以最好就判断是否为0就可以了，实在要判断自己写的c程序返回值，建议返回0,1,2,3等值，出错返回 -1。
另外，我遇到一次明明处理好了返回值，c程序调试信息提示也该返回值0了，结果python获取到的是 -1，而且无论c程序返回多少，python都获取-1。后来排查c程序的问题，发现原来是因为我这个python程序本身是由另一个C程序调用的，而调 用它的那个C程序中将SIGCLD信号忽略了（这表明python是根据子进程退出时产生的信号来获取返回值的），我将那个C程序的SIGCLD绑定到函 数，即使那个函数什么也不做，python也能获取到正确的返回值了。
/**********************************************************************************************************************/
linux命令执行后无论成功与否都有一个返回值：
如果为 0，则表示命令执行成功，其它值则表示错误，具体的错误码含义如下：
"OS error code 1:Operation not permitted"
"OS error code 2:No such file or directory"
"OS error code 3:No such process"
"OS error code 4:Interrupted system call"
"OS error code 5:Input/output error"
"OS error code 6:No such device or address"
"OS error code 7:Argument list too long"
"OS error code 8:Exec format error"
"OS error code 9:Bad file descriptor"
"OS error code10:No child processes"
"OS error code11:Resource temporarily unavailable"
"OS error code12:Cannot allocate memory"
"OS error code13:Permission denied"
"OS error code14:Bad address"
"OS error code15:Block device required"
"OS error code16:Device or resource busy"
"OS error code17:File exists"
"OS error code18:Invalid cross-device link"
"OS error code19:No such device"
"OS error code20:Not a directory"
"OS error code21:Is a directory"
"OS error code22:Invalid argument"
"OS error code23:Too many open files in system"
"OS error code24:Too many open files"
"OS error code25:Inappropriate ioctl for device"
"OS error code26:Text file busy"
"OS error code27:File too large"
"OS error code28:No space left on device"
"OS error code29:Illegal seek"
"OS error code30:Read-only file system"
"OS error code31:Too many links"
"OS error code32:Broken pipe"
"OS error code33:Numerical argument out of domain"
"OS error code34:Numerical result out of range"
"OS error code35:Resource deadlock avoided"
"OS error code36:File name too long"
"OS error code37:No locks available"
"OS error code38:Function not implemented"
"OS error code39:Directory not empty"
"OS error code40:Too many levels of symbolic links"
"OS error code42:No message of desired type"
"OS error code43:Identifier removed"
"OS error code44:Channel number out of range"
"OS error code45:Level 2 not synchronized"
"OS error code46:Level 3 halted"
"OS error code47:Level 3 reset"
"OS error code48:Link number out of range"
"OS error code49:Protocol driver not attached"
"OS error code50:No CSI structure available"
"OS error code51:Level 2 halted"
"OS error code52:Invalid exchange"
"OS error code53:Invalid request descriptor"
"OS error code54:Exchange full"
"OS error code55:No anode"
"OS error code56:Invalid request code"
"OS error code57:Invalid slot"
"OS error code59:Bad font file format"
"OS error code60:Device not a stream"
"OS error code61:No data available"
"OS error code62:Timer expired"
"OS error code63:Out of streams resources"
"OS error code64:Machine is not on the network"
"OS error code65:Package not installed"
"OS error code66:Object is remote"
"OS error code67:Link has been severed"
"OS error code68:Advertise error"
"OS error code69:Srmount error"
"OS error code70:Communication error on send"
"OS error code71:Protocol error"
"OS error code72:Multihop attempted"
"OS error code73:RFS specific error"
"OS error code74:Bad message"
"OS error code75:Value too large for defined data type"
"OS error code76:Name not unique on network"
"OS error code77:File descriptor in bad state"
"OS error code78:Remote address changed"
"OS error code79:Can not access a needed shared library"
"OS error code80:Accessing a corrupted shared library"
"OS error code81:.lib section in a.out corrupted"
"OS error code82:Attempting to link in too many shared libraries"
"OS error code83:Cannot exec a shared library directly"
"OS error code84:Invalid or incomplete multibyte or wide character"
"OS error code85:Interrupted system call should be restarted"
"OS error code86:Streams pipe error"
"OS error code87:Too many users"
"OS error code88:Socket operation on non-socket"
"OS error code89:Destination address required"
"OS error code90:Message too long"
"OS error code91:Protocol wrong type for socket"
"OS error code92:Protocol not available"
"OS error code93:Protocol not supported"
"OS error code94:Socket type not supported"
"OS error code95:Operation not supported"
"OS error code96:Protocol family not supported"
"OS error code97:Address family not supported by protocol"
"OS error code98:Address already in use"
"OS error code99:Cannot assign requested address"
"OS error code 100:Network is down"
"OS error code 101:Network is unreachable"
"OS error code 102:Network dropped connection on reset"
"OS error code 103:Software caused connection abort"
"OS error code 104:Connection reset by peer"
"OS error code 105:No buffer space available"
"OS error code 106:Transport endpoint is already connected"
"OS error code 107:Transport endpoint is not connected"
"OS error code 108:Cannot send after transport endpoint shutdown"
"OS error code 109:Too many references: cannot splice"
"OS error code 110:Connection timed out"
"OS error code 111:Connection refused"
"OS error code 112:Host is down"
"OS error code 113:No route to host"
"OS error code 114:Operation already in progress"
"OS error code 115:Operation now in progress"
"OS error code 116:Stale NFS file handle"
"OS error code 117:Structure needs cleaning"
"OS error code 118:Not a XENIX named type file"
"OS error code 119:No XENIX semaphores available"
"OS error code 120:Is a named type file"
"OS error code 121:Remote I/O error"
"OS error code 122:Disk quota exceeded"
"OS error code 123:No medium found"
"OS error code 124:Wrong medium type"
"OS error code 125:Operation canceled"
"OS error code 126:Required key not available"
"OS error code 127:Key has expired"
"OS error code 128:Key has been revoked"
"OS error code 129:Key was rejected by service"
"OS error code 130:Owner died"
"OS error code 131:State not recoverable"
python运算符空串、None、0还有一些表示空性值的会转换为False，其余全部都是True.
逻辑与都为True时为True,如果有一个False 就是False
a=True and True 得True
b=True and False 得False
c=False and False 得True
逻辑或
a=True or True 得True
b=True orFalse 得True
c=False or False 得False
与运算规则是找False,如果第一个值是False 那么不瞅第二个值，直接输出第一个值，如果第一个值是True,那么直接输出第二个值。
a=1 and 2 得2
a=0 and 2 得0
a=None and 0 得None
a=25 and 254 得254
a=0 and 34 得0
或运算规则是找True,如果第一个值是True 那么不瞧第二个值，直接输出第一个值，如果第一个是值是False,那么直接输出第二个值
a=1 or 2 得 1
a= False or 1 得 1
a= 0 or None 得None
根椐查表判断运算符优先级，and 优先级高于or
r=34 and 89 or 63 得 89
r=0 and 89 or 63 得63
r=None and 89 or 63 得63
r=78 and False or 63 得63
语法：语句1 if 条件表达式 else 语句2
a=25
b=14
c=a if ab else b
print(c)
25
name='521 {}嫁给我好吗？'.format('王奕菲')
name1='521 %s嫁给我好吗？'%'王奕菲'
a='王奕菲'
name2=f'521 {a}嫁给我好吗？'
b='521'
c='嫁给我好吗？'
name3=b+' '+a+c
print(name)
print(name1)
print(name2)
print(name3)
a=54
b=23
c=87
d = a if ab else b
e = c if cd else d
print(e)
<2024-09-19