Question

我目前正在python中执行if then else语句，但我有symbolUpper的30个条件：

if symbolUpper == "CAT":
    growth = (((listOfRecords[2][5]-listOfRecords[2][4])/listOfRecords[2][4])*100)
    peRatio = (listOfRecords[2][5]/listOfRecords[2][6])
    print("Company: " + listOfRecords[2][0])
    print("Industry: " + listOfRecords[2][3])
    print("Exchange: " + listOfRecords[2][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

是否有更简单的方法在python中编码而不列出所有30个条件？我还包括了我的整个代码。

infile = open("Dow.txt", 'r')
listOfRecords = [line.rstrip() for line in infile]
infile.close()
for i in range(len(listOfRecords)):
    listOfRecords[i]=listOfRecords[i].split(",")
    listOfRecords[i][4] = eval(listOfRecords[i][4])     # price at the end of trading on 12/31/2012
    listOfRecords[i][5] = eval(listOfRecords[i][5])     # price at the end of trading on 12/31/2013
    listOfRecords[i][6] = eval(listOfRecords[i][6])     # 2013 earnings per share

print("Symbols for the Thirty DOW Stocks")
print(listOfRecords[0][1] + "\t" + listOfRecords[1][1] + "\t" +
      listOfRecords[2][1] + "\t" + listOfRecords[3][1] + "\t" +
      listOfRecords[4][1] + "\t" + listOfRecords[5][1] + "\t" +
      listOfRecords[6][1] + "\t" + listOfRecords[7][1] + "\t" +
      listOfRecords[8][1] + "\t" + listOfRecords[9][1] + "\n" +
      listOfRecords[10][1] + "\t" + listOfRecords[11][1] + "\t" +
      listOfRecords[12][1] + "\t" + listOfRecords[13][1] + "\t" +
      listOfRecords[14][1] + "\t" + listOfRecords[15][1] + "\t" +
      listOfRecords[16][1] + "\t" + listOfRecords[17][1] + "\t" +
      listOfRecords[18][1] + "\t" + listOfRecords[19][1] + "\n" +
      listOfRecords[20][1] + "\t" + listOfRecords[21][1] + "\t" +
      listOfRecords[22][1] + "\t" + listOfRecords[23][1] + "\t" +
      listOfRecords[24][1] + "\t" + listOfRecords[25][1] + "\t" +
      listOfRecords[26][1] + "\t" + listOfRecords[27][1] + "\t" +
      listOfRecords[28][1] + "\t" + listOfRecords[29][1] + "\t")
print()
symbol = input("Enter a symbol: ")
symbolUpper = symbol.upper()

if symbolUpper == "AXP":
    growth = (((listOfRecords[0][5]-listOfRecords[0][4])/listOfRecords[0][4])*100)
    peRatio = (listOfRecords[0][5]/listOfRecords[0][6])
    print("Company: " + listOfRecords[0][0])
    print("Industry: " + listOfRecords[0][3])
    print("Exchange: " + listOfRecords[0][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

if symbolUpper == "BA":
    growth = (((listOfRecords[1][5]-listOfRecords[1][4])/listOfRecords[1][4])*100)
    peRatio = (listOfRecords[1][5]/listOfRecords[1][6])
    print("Company: " + listOfRecords[1][0])
    print("Industry: " + listOfRecords[1][3])
    print("Exchange: " + listOfRecords[1][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

if symbolUpper == "CAT":
    growth = (((listOfRecords[2][5]-listOfRecords[2][4])/listOfRecords[2][4])*100)
    peRatio = (listOfRecords[2][5]/listOfRecords[2][6])
    print("Company: " + listOfRecords[2][0])
    print("Industry: " + listOfRecords[2][3])
    print("Exchange: " + listOfRecords[2][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

if symbolUpper == "CSCO":
    growth = (((listOfRecords[3][5]-listOfRecords[3][4])/listOfRecords[3][4])*100)
    peRatio = (listOfRecords[3][5]/listOfRecords[3][6])
    print("Company: " + listOfRecords[3][0])
    print("Industry: " + listOfRecords[3][3])
    print("Exchange: " + listOfRecords[3][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

Answer 1

是。有。使用dict：

维护您的符号查找

lookup_dict = {'AXP': 0, 'BA': 1, ...}
try:
    i = lookup_dict[symbolUpper]
    growth = (((listOfRecords[i][5]-listOfRecords[i][4])/listOfRecords[i][4])*100)
    peRatio = (listOfRecords[i][5]/listOfRecords[i][6])
    print("Company: " + listOfRecords[i][0])
    print("Industry: " + listOfRecords[i][3])
    print("Exchange: " + listOfRecords[i][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))
except KeyError:
    ... # symbolUpper not in dict

Answer 2

当你有重复时，看看有什么相同，有什么不同。

将两者分开。

唯一不同的是索引。有许多相同的部分。

如果您复制并粘贴了一次或两次以上，则需要重新考虑。正如他们所说，三次罢工，你重构。

您的代码也非常详细。例如，listOfRecords会更好，只有records。您还可以直接迭代数据，而不是迭代范围并索引到数据中：

print("Symbols for the Thirty DOW Stocks")
print('\t'.join(record[1] for record in records)

当您打开文件时，最好在之后关闭它。如果您使用with语句，Python将自动为您执行此操作。此外，默认情况下模式为r，因此您无需指定它：

with open("Dow.txt") as infile:
    records = [line.rstrip() for line in infile]
# file will be closed here

你不应该使用eval。例如，如果输入包含删除所有文件的命令，则可能会造成严重破坏。如果您只有字面数字，则可以安全地使用literal_eval：

from ast import literal_eval

records = [records.split(',') for record in records]
for record in records:
    record[4] = literal_eval(record[4])  # price at the end of trading on 12/31/2012
    record[5] = literal_eval(record[5])  # price at the end of trading on 12/31/2013
    record[6] = literal_eval(record[6])  # 2013 earnings per share

解决重复和索引的问题。记录包含库存的符号，因此您可以使用记录构建查找表。在Python中，查找表最好用dict表示：

lookup = {record[1]: record
          for record in records}

旁白：现在我们有一个基于DOW符号的查找表，我们可以在打印符号时使用它，因为迭代字典会给你键（这是DOW符号）：

print("Symbols for the Thirty DOW Stocks")
print('\t'.join(symbol for symbol in records)

您可以使用以下函数替换其余代码：

def report(dow):
    growth = 100 * (dow[5] - dow[4]) / dow[4]
    peRatio = dow[5] / dow[6]
    print("Company: " + dow[0])
    print("Industry: " + dow[3])
    print("Exchange: " + dow[2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

您可以将其称为：

report(lookup[symbol])

进一步的改进包括使用csv模块，当您手动执行split(',')时，它可以为您执行此操作。此外，它正确处理引用字段，因此如果您的公司名称中包含任何逗号，例如Google，Inc，如果它被引用为“Google，Inc”csv将会处理它而不会在逗号上拆分：

import csv

with open("Dow.txt") as infile:
    records = list(csv.reader(infile))

此外，namedtuple可与csv条记录完美配合。

Dow = namedtuple('Dow', 'company symbol exchange industry previous price earning')

records = [Dow(*[literal_eval(value) for value in record])
           for record in records]

然后您的计算可以更容易阅读：

growth = 100 * (dow.price - dow.previous) / dow.previous
pe_ratio = dow.price / dow.earning

最后，您的报告应与print分开，因为您可能希望在其他地方使用它，例如记录，写入文件等。使用格式字段也使其更具可读性。

report_format = ('Company: {dow.company}\n'
                 'Industry: {dow.industry}\n'
                 'Exchange: {dow.exchange}\n'
                 'Growth in 2013: {growth:,.2f}%\n'
                 'Price/Earning ratio in 2013@ {pe_ratio:,.2f}\n')

report = report_format.format(dow=record,
                              growth=growth,
                              pe_ratio=pe_ratio)

print(report)

Answer 3

将所有要比较的字符串保存在列表中，然后获取所需字符串的索引并使用该索引执行任务。

symbolUpperList = ["AXP", "BA", "CAT", ...]

i = symbolUpperList.index(symbolUpper)
growth = (((listOfRecords[i][5]-listOfRecords[i][4])/listOfRecords[i][4])*100)
peRatio = (listOfRecords[i][5]/listOfRecords[i][6])
print("Company: " + listOfRecords[i][0])
print("Industry: " + listOfRecords[i][3])
print("Exchange: " + listOfRecords[i][2])
print("Growth in 2013: {0:,.2f}%".format(growth))
print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

Answer 4

使用键和值准备symbolUpper数据库。
将您的实际代码移至功能。
使用symbolUpper的id

代码如下：

infile = open("Dow.txt", 'r')
listOfRecords = [line.rstrip() for line in infile]

symbolUpper_db = {"AXP": 1, "BA" : 2, "CAT":3, "CSCO":4 }

def compute( symbol_idx ):
    growth = (((listOfRecords[symbol_idx][5]-listOfRecords[symbol_idx][4])/listOfRecords[symbol_idx][4])*100)
    peRatio = (listOfRecords[symbol_idx][5]/listOfRecords[symbol_idx][6])
    print("Company: " + listOfRecords[symbol_idx][0])
    print("Industry: " + listOfRecords[symbol_idx][3])
    print("Exchange: " + listOfRecords[symbol_idx][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

compute(symbolUpper_db[symbolUpper])

Answer 5

您的passport.use( new LocalStrategy({ usernameField: 'email', passwordField: 'password', passReqToCallback: true }, function(request, email, password, done) { process.nextTick(function() { User.findOne({ username }, function(err, user) { if (err) { return done(err); } else if (!users.length) { return done(null, false, { errorUsername: "user doesnt exist" }); } else { var user = users[0]; bcrypt.compare(password, user.password, function(err, res) { if (res) { return done(null, user); } else { return done(null, false); } }); } } }); } }); }); }) );只有更改。所以为每个index

指定索引

这是简单的if条件，

symbolUpper symbolUpper ==＆＃34; AXP＆＃34;否则错误

i = 2 if symbolUpper == "CAT" else 1 if symbolUpper == "BA" else 0 if

或者您可以尝试使用词典查找，

if i:
    growth = (((listOfRecords[i][5]-listOfRecords[i][4])/listOfRecords[i][4])*100)
    peRatio = (listOfRecords[i][5]/listOfRecords[i][6])
    print("Company: " + listOfRecords[i][0])
    print("Industry: " + listOfRecords[i][3])
    print("Exchange: " + listOfRecords[i][2])
    print("Growth in 2013: {0:,.2f}%".format(growth))
    print("Price/Earning ratio in 2013: {0:,.2f}".format(peRatio))

如果then else语句为python中的多个条件

5 个答案: