我想使用subprocess.Popen()从python脚本调用bash脚本。将shell脚本作为可执行文件调用是可行的，但是source不能。为什么？为什么？
文件 test_python.py：

import sys
import os
import subprocess

os.putenv("testvar", "testvalue")

test = subprocess.Popen("./test_shell.sh", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
print(test)
test = subprocess.Popen(". test_shell.sh", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
print(test)
test = subprocess.Popen("source test_shell.sh", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
print(test)
test = subprocess.Popen("/bin/bash test_shell.sh", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
print(test)
test = subprocess.Popen("/bin/sh test_shell.sh", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
print(test)

字符串
文件 test_shell.sh：

#!/bin/bash

echo "$testvar"

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python test_python.py的输出：

('testvalue\n', '')
('', '/bin/sh: .: test_shell.sh: cannot open [No such file or directory]\n')
('', '/bin/sh: .: test_shell.sh: cannot open [No such file or directory]\n')
('testvalue\n', '')
('testvalue\n', '')

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