爲什麼我的Python函數被跳過？

Question

我有一個試圖執行外部命令的小腳本。但由於某種原因，我執行該命令的功能正在被完全跳過！似乎沒有錯誤提出，它只是不執行。我在裏面有一些調試打印語句來驗證函數是否進入，但他們從不打印。我在它外面有一個打印語句來驗證腳本沒有死掉。那麼是什麼給了？

from xml.etree import ElementTree as et 
import subprocess 

pomFileLocation = "pom.xml" 
uiAutomationCommand = "mvn clean install" 
revertPomFileCommand = "git checkout pom.xml" 
profileToSetToDefault = "smoketest" 

def modifyxml(datafile, value): 
    print("modifying " + datafile) 
    tree = et.parse(datafile) 
    rootNodes = tree.getroot() 
    for node in rootNodes: 
     if "profiles" in node.tag: 
      for profile in node.iter(): 
       foundIt = False 
       for param in profile.iter(): 
        if "id" in param.tag and profileToSetToDefault in param.text: 
         foundIt = True 
         break 
       if foundIt == True: 
        for param in profile.iter(): 
         if "activation" in param.tag: 
          for child in param.iter(): 
           if "activeByDefault" in child.tag: 
            child.text = value 
            tree.write(datafile) 
            return 

def runExternalCommand(comm): 
    print("running command " + comm) 
    p = subprocess.Popen(comm, bufsize=-1, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()[0] 
    print(str(p)) 
    while(True): 
     print("still running") 
     retcode = p.poll() 
     line = p.stdout.readline() 
     yield line 
     if(retcode is not None): 
      print("Exiting") 
      break 
    return 

if __name__ == '__main__': 
    modifyxml(pomFileLocation, "true") 
    #runExternalCommand(uiAutomationCommand) 
    runExternalCommand(revertPomFileCommand) 
    print("finished") 

Answer 1

runExternalCommand使用yield，所以如果你希望它一路執行到底，你應該稱呼它for something in runExternalCommand(revertPomFileCommand):。或者直接刪除yield這一行，因爲你似乎並不需要它。

def runExternalCommand(comm): 
    print("running command " + comm) 
    p = subprocess.Popen(comm, bufsize=-1, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()[0] 
    print(str(p)) 
    while(True): 
     print("still running") 
     retcode = p.poll() 
     line = p.stdout.readline() 
     yield line 
     if(retcode is not None): 
      print("Exiting") 
      break 
    return 

if __name__ == '__main__': 
    modifyxml(pomFileLocation, "true") 
    #runExternalCommand(uiAutomationCommand) 
    for line in runExternalCommand(revertPomFileCommand): 
     pass 
    print("finished") 

或者

def runExternalCommand(comm): 
    print("running command " + comm) 
    p = subprocess.Popen(comm, bufsize=-1, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()[0] 
    print(str(p)) 
    while(True): 
     print("still running") 
     retcode = p.poll() 
     line = p.stdout.readline() 
     if(retcode is not None): 
      print("Exiting") 
      break 
    return 

if __name__ == '__main__': 
    modifyxml(pomFileLocation, "true") 
    #runExternalCommand(uiAutomationCommand) 
    runExternalCommand(revertPomFileCommand) 
    print("finished") 

Answer 2

由於@Kevin said，主要（但不是唯一的）問題是runExternalCommand是發電機。要消耗它，你可以運行：print(list(runExternalCommand(revertPomFileCommand)))。

雖然功能runExternalCommand()被打破：沒有一點叫p.stdout.readline()後.communicate()回報（子進程結束後等待並立即返回整個輸出）。

目前尚不清楚你想要得到例如，運行git命令和存儲其在一個可變輸出什麼結果，你可以使用subprocess.check_output()：

from subprocess import check_output, STDOUT 

output = check_output("git checkout pom.xml".split(), 
         stderr=STDOUT, universal_newlines=True) 

要放棄孩子的標準輸出/標準錯誤，而不是保存，使用subprocess.check_call()：

from subprocess import check_call, DEVNULL, STDOUT 

check_call("git checkout pom.xml".split(), 
      stdout=DEVNULL, stderr=STDOUT) 

對於代碼示例，以讀取輸出，同時子進程仍在運行，見Constantly print Subprocess output while process is running。