Python:如何在小于目标的列表中查找值

Question

例如，我有一个未排序的值列表 [10, 20, 50, 200, 100, 300, 250, 150]

我有这段代码返回下一个更大的值:

def GetNextHighTemp(self,  temp,  templist):
    target = int(temp)
    list = []
    for t in templist:
        if t != "":
            list.append(int(t))
    return str(min((abs(target - i), i) for i in list)[1])

例如如果 temp = 55，它将返回“100”。

但是我怎样才能得到较小的值呢？那就是如何让它返回'50'？

谢谢。

编辑 - 现在工作

def OnTWMatCurrentIndexChanged(self):
    self.ClearTWSelectInputs()
    material = self.cb_TW_mat.currentText()
    temp = self.txt_design_temp.text()
    if material != "":
        Eref = self.GetMaterialData(material,  "25",  "elast")
        if Eref and Eref != "":
            Eref = str(float(Eref) / 1000000000)
            self.txt_TW_Eref.setText(Eref)
        else:
            self.txt_TW_Eref.setText("194.8")
            self.ShowMsg("No temperature match found for E<sub>ref</sub> in material data file. Value of 194.8 GPa will be used.",  "blue")
    if material != "" and temp != "":
        if self.CheckTWTemp(material,  temp):
            dens = self.GetMaterialData(material,  temp,  "dens")
            self.txt_TW_dens.setText(dens)
            elast = self.GetMaterialData(material,  temp,  "elast")
            elast = str(float(elast) / 1000000000)
            self.txt_TW_Et.setText(elast)
            stress = self.GetMaterialData(material,  temp,  "stress")
            stress = str(float(stress) / 1000000)
            self.txt_TW_stress_limit.setText(stress)
        else:
            self.ShowMsg("No temperature match found for " + temp + "&#x00B0; C in material data file. Extrapolated data will be used where possible or add new material data.",  "blue")
            dens = self.GetExtrapolatedMaterialData(material,  temp,  "dens")
            self.txt_TW_dens.setText(dens)
            elast = self.GetExtrapolatedMaterialData(material,  temp,  "elast")
            elast = str(float(elast) / 1000000000)
            self.txt_TW_Et.setText(elast)
            stress = self.GetExtrapolatedMaterialData(material,  temp,  "stress")
            stress = str(float(stress) / 1000000)
            self.txt_TW_stress_limit.setText(stress)
    else:
        self.ClearTWSelectInputs()

def CheckTWTemp(self, matvar, tempvar):
    for material in self.materials:
        if material.attrib["name"] == matvar:
            temps = material.getiterator("temp")
            for temp in temps:
                if int(temp.text) == int(tempvar):
                    return True
            return False

def GetMaterialData(self, matvar, tempvar, tag):
    for material in self.materials:
        if material.attrib["name"] == matvar:
            temps = material.getiterator("temp")
            for temp in temps:
                if temp.text == tempvar:
                    value = temp.find(tag)
                    return value.text

def GetExtrapolatedMaterialData(self, matvar, tempvar, tag):
    try:
        templist = QStringList()
        for material in self.materials:
            if material.attrib["name"] == matvar:
                temps = material.getiterator("temp")
                for temp in temps:
                    templist.append(temp.text)
        templist.sort()
        target = int(tempvar)
        x1 = max(int(t) for t in templist if t != '' and int(t) < target)
        x2 = min(int(t) for t in templist if t != '' and int(t) > target)
        y1 = float(self.GetMaterialData(matvar, str(x1), tag))
        y2 = float(self.GetMaterialData(matvar, str(x2), tag))
        x = target
        y = y1 - ((y1 - y2) * (x - x1) / (x2 - x1))
        return str(y)
    except Exception, inst:
        return "0"

Answer 1

更好更快(代码和 cpu 明智)的方法是使用 bisect 模块进行二进制搜索，但为此您需要先对列表进行排序，这是示例用法:

import bisect

mylist = [10, 20, 50, 200, 100, 300, 250, 150]
mylist.sort()

index = bisect.bisect(mylist, 55)
print "Greater than target", mylist[index]
print "Smaller than or equal to target", mylist[index-1]

输出:

Greater than target 100
Smaller than or equal to target 50

您还需要检查返回的索引，如果它是0，则表示您已通过低于最低的目标