Python代码报错：'str'无decode属性及语法错误求解

问题描述 #

运行基于日语WordNet的Python代码时遇到以下两个错误：

• 执行words = getWords(sys.argv[1].decode(sys.stdin.encoding))时，触发AttributeError: 'str' object has no attribute 'decode'
• 移除decode调用后，出现SyntaxError: invalid syntax，错误指向if words:行

错误1：AttributeError: 'str' object has no attribute 'decode' #

原因

Python 3中，sys.argv传入的命令行参数已经是Unicode字符串（str类型），而decode()是Python 2中bytes类型的方法，Python 3的str对象没有这个属性，因此调用会报错。

解决方法

直接删除.decode(sys.stdin.encoding)，修改为：

words = getWords(sys.argv[1])

错误2：SyntaxError: invalid syntax #

原因

代码使用了Python 2的语法特性，在Python 3环境下无法解析：

1. Python 2的print >>sys.stderr, "(nothing found)"是语句写法，Python 3中print是内置函数，必须用括号包裹参数并指定file参数输出到标准错误流；
2. len(sys.argv)>=3 and sys.argv[2] or 'hypo'属于不规范写法，容易引发逻辑歧义。

解决方法

1. 将标准错误输出的print语句修改为Python 3格式：

   # 原Python 2写法
   print >>sys.stderr, "(nothing found)"
   # 修改为Python 3写法
   print("(nothing found)", file=sys.stderr)
   

2. 用三元表达式替换and/or的条件赋值写法，提升可读性：

   # 原写法
   link = len(sys.argv)>=3 and sys.argv[2] or 'hypo'
   lang = len(sys.argv)==4 and sys.argv[3] or 'jpn'
   # 修改为三元表达式
   link = sys.argv[2] if len(sys.argv) >= 3 else 'hypo'
   lang = sys.argv[3] if len(sys.argv) == 4 else 'jpn'
   

完整修正后的代码 #

#!/usr/bin/env python3
# encoding: utf-8
import sys
import sqlite3
from collections import namedtuple

conn = sqlite3.connect("wnjpn.db")

Word = namedtuple('Word', 'wordid lang lemma pron pos')

def getWords(lemma):
    cur = conn.execute("select * from word where lemma=?", (lemma,))
    return [Word(*row) for row in cur]

def getWord(wordid):
    cur = conn.execute("select * from word where wordid=?", (wordid,))
    return Word(*cur.fetchone())
 
Sense = namedtuple('Sense', 'synset wordid lang rank lexid freq src')

def getSenses(word):
    cur = conn.execute("select * from sense where wordid=?", (word.wordid,))
    return [Sense(*row) for row in cur]

def getSense(synset, lang='jpn'):
    cur = conn.execute("select * from sense where synset=? and lang=?",
                     (synset, lang))
    row = cur.fetchone()
    return Sense(*row) if row else None

Synset = namedtuple('Synset', 'synset pos name src')

def getSynset(synset):
    cur = conn.execute("select * from synset where synset=?", (synset,))
    return Synset(*cur.fetchone())

SynLink = namedtuple('SynLink', 'synset1 synset2 link src')

def getSynLinks(sense, link):
    cur = conn.execute("select * from synlink where synset1=? and link=?",
                     (sense.synset, link))
    return [SynLink(*row) for row in cur]

def getSynLinksRecursive(senses, link, lang='jpn', _depth=0):
    for sense in senses:
        synLinks = getSynLinks(sense, link)
        if synLinks:
            print(''.join([' '*2*_depth,
                           getWord(sense.wordid).lemma,
                           ' ',
                           getSynset(sense.synset).name]))
        _senses = []
        for synLink in synLinks:
            sense = getSense(synLink.synset2, lang)
            if sense:
                _senses.append(sense)
        
        getSynLinksRecursive(_senses, link, lang, _depth+1)

def getWordsFromSynset(synset, lang):
    cur = conn.execute("select word.* from sense, word where synset=? and word.lang=? and sense.wordid = word.wordid;", (synset, lang))
    return [Word(*row) for row in cur]

def getWordsFromSenses(sense, lang):
    for s in sense:
        print(getSynset(s.synset).name)
        syns = getWordsFromSynset(s.synset, lang)
        for sy in syns:
            print('  ' + sy.lemma)


if __name__ == '__main__':
    if len(sys.argv) >= 3:
        words = getWords(sys.argv[1])
        if words:
            for w in words:
                sense = getSenses(w)
                link = sys.argv[2] if len(sys.argv) >= 3 else 'hypo'
                lang = sys.argv[3] if len(sys.argv) == 4 else 'jpn'
                if link == 'syns':
                    getWordsFromSenses(sense, lang)
                else:
                    getSynLinksRecursive(sense, link, lang)
        else:
            print("(nothing found)", file=sys.stderr)
    else:
        print("usage: python jpWordnet.py ピラミッド syns")

内容的提问来源于stack exchange，提问作者jms