Mastering Python Built‑ins: print, input, open, eval, and exec for Test Automation

print()

Customize console output using the sep parameter to join objects with a chosen delimiter and the end parameter to suppress the trailing newline.

# basic usage (default space separator, newline at end)
print("接口登录测试", "状态码:200", "耗时:0.5s")

# advanced usage: custom separator and no newline (useful for progress bars)
print("2026-07-11", "POST /api/login", "200 OK", sep=" | ", end=" >>> ")
print("断言通过")

Redirect output to a file with the file argument inside a context manager.

# write to a file and auto‑close
with open("test_report.txt", "w", encoding="utf-8") as f:
    print("测试用例1：登录接口", file=f)
    print("测试结果：PASS", file=f)

# append mode with explicit flush to avoid log loss
with open("test_report.txt", "a", encoding="utf-8") as f:
    print("测试用例2：订单接口", "FAIL", sep=" | ", file=f, flush=True)

input()

Collect user input; the function always returns a string. A prompt can be supplied.

# simple prompt
env = input("请输入要测试的环境 (test/prod): ")
print(f"即将开始 {env} 环境的接口测试...")

# obtain multiple values in one line and split them
info = input("请输入 接口路径 和 期望状态码 (空格分隔): ").split()
print(f"准备测试接口: {info[0]}，期望状态码: {info[1]}")

Validate numeric input with try‑except and repeat until a valid value is entered.

# basic validation
try:
    threads = int(input("请输入并发线程数: "))
    print(f"设置线程数为: {threads}")
except ValueError:
    print("输入无效，必须是纯数字！")

# loop until a positive integer is provided
while True:
    try:
        timeout = int(input("请输入接口超时时间(秒): "))
        if timeout > 0:
            break
        print("超时时间必须大于0，请重新输入")
    except ValueError:
        print("格式错误，请输入整数")
print(f"超时时间已设置为: {timeout}秒")

open()

Read configuration files line‑by‑line, optionally filtering comment lines that start with #.

# simple line reading
with open("config.txt", "r", encoding="utf-8") as f:
    for line in f:
        print(f"读取到接口: {line.strip()}")

# filter out empty lines and comments
with open("config.txt", "r", encoding="utf-8") as f:
    apis = [line.strip() for line in f if line.strip() and not line.startswith("#")]
    print(f"有效接口数量: {len(apis)}")

Append test execution details to a log file.

# append mode using write()
with open("run.log", "a", encoding="utf-8") as f:
    f.write("2026-07-11 10:00:00 | /api/user | PASS
")

# append mode using print(..., file=f)
with open("run.log", "a", encoding="utf-8") as f:
    print("2026-07-11", "/api/order", "FAIL", "耗时:2.1s", sep=" | ", file=f)

eval()

Convert a string representation of a Python literal into an actual object, perform simple calculations, or evaluate dynamic assertions.

# string to dict
resp_str = '{"code": 200, "msg": "success"}'
resp_dict = eval(resp_str)
print(f"状态码是: {resp_dict['code']}")

# simple arithmetic
calc_str = "100 * 2 + 50"
result = eval(calc_str)
print(f"接口响应计算结果: {result}")

# dynamic boolean assertion
response = {"age": 20}
assertion = "response['age'] > 18"
print(f"断言结果: {eval(assertion)}")

# safe eval with restricted globals
safe_dict = {"__builtins__": {}}
result = eval("response['age'] == 20", safe_dict, {"response": response})
print(f"安全断言结果: {result}")

# extract nested field
data = {"user": {"name": "Alice", "age": 25}}
path = "data['user']['name']"
print(f"提取到的名字: {eval(path)}")

# batch conversion from a file where each line is a dict string
with open("data.txt", "r") as f:
    dataset = [eval(line.strip()) for line in f if line.strip()]
    print(f"共加载 {len(dataset)} 条测试数据")

exec()

Execute arbitrary Python code strings, dynamically define functions or classes, and load external scripts.

# execute a multi‑line snippet
code = "x = 10
y = 20
print(f'动态计算和: {x+y}')"
exec(code)

# load an external helper file
with open("auth_helper.py", "r") as f:
    exec(f.read())
print("鉴权模块加载完毕")

# execute code in a custom namespace and retrieve variables
namespace = {}
exec("BASE_URL = 'https://api.test.com'
TIMEOUT = 30", namespace)
print(f"加载的配置: {namespace['BASE_URL']}")

# dynamically define a test function
func_code = "def test_login():
    assert 1 + 1 == 2"
exec(func_code)
test_login()
print("动态函数执行成功")

# generate multiple test functions in a loop
for i in range(3):
    exec(f"def test_api_{i}():
    print(f'正在执行接口 {i}')")

test_api_0()
test_api_1()

Combined built‑ins for interactive tools and reports

Build a simple interactive menu with print and input, and generate a Markdown‑style test report using exec.

# interactive menu
while True:
    print("
=== 自动化测试工具箱 ===")
    print("1. 造数据  2. 跑回归  3. 退出")
    opt = input("请选择: ").strip()
    if opt == '3':
        print("已退出")
        break
    elif opt in ('1', '2'):
        print(f"正在执行任务 {opt}…")
    else:
        print("无效选项，请重新输入")

# dynamic report generation
report_code = "print('--- 测试报告 ---')
print('通过: 10, 失败: 2')"
exec(report_code)

results = {"pass": 10, "fail": 2}
code = f"print(f'通过率: {results['pass']}/(results['pass']+results['fail'])*100:.1f}%')"
exec(code)

Practical notes

Use eval and exec only with trusted code; they can execute arbitrary commands.

Avoid input() in CI/CD pipelines because the process will block without a console.

When writing logs with print(..., file=f), enable flush=True to ensure data is persisted on crashes.